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7mm-08 in a AR platform

fmsniper

1st Sergeant
Full Member
Minuteman
So Thanksgiving break is coming, I needed a project, I have a 2-308 and a 260 AR, so I have decided to buy a Bartlien Blank and make a 22 -24 in barrel for my AR10(DPMS) and chamber it in 7mm-08
not sure why just never see them...I know R25 in a 20 inch is out there but I figure with a Premium barrel and slightly longer, it may be a winner
 
I think 7mm-08 is what the .308 should have been, although I would be more interested in what you could do with a lightweight DM Carbine project.

Looking at the 162gr pills, you would crush the 175gr .308 SMK. The 162gr A-MAX has a BC of .625 G1! The 162gr SST is .540...

A really cool challenge for a smith would be to see how well you could lighten the receivers, lighten the barrel profile without ruining accuracy, and what the optimum barrel length and gun balance is for a long-range capable, DMC based on the T65 case in 7mm. Do you already have receivers and BCG? This is what I'm referring to:



We already know what a 22" to 24" 7-08 will do, and it's nothing to laugh at, but nobody has really put forth a good 7mm-08 AR10 carbine. I think they're meant for each other.
 
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Big fan of the 7mm bullets from all I've read. Too bad the SAUMs in .308-sized ARs never really caught on and that I'm so late to the firearms ownership party - a 7mm SAUM in a semi-auto seems like it would have been a hoot.
 
I picked up a second DPMS complete 308 18 inch barrel rifle yesterday so yes I have a complete rifle to use as my platform, I already have the stainless barrel extension I would need more information on the 7mm-08 and barrel length!!!! so farwhat I have found is 22 inch is the accuracy node?


I may do like I did with the grendel and begin at 24 and cut it down an inch at a time to find the sweat spot

I think 7mm-08 is what the .308 should have been, although I would be more interested in what you could do with a lightweight DM Carbine project.

Looking at the 162gr pills, you would crush the 175gr .308 SMK. The 162gr A-MAX has a BC of .625 G1! The 162gr SST is .540...

A really cool challenge for a smith would be to see how well you could lighten the receivers, lighten the barrel profile without ruining accuracy, and what the optimum barrel length and gun balance is for a long-range capable, DMC based on the T65 case in 7mm. Do you already have receivers and BCG? This is what I'm referring to:



We already know what a 22" to 24" 7-08 will do, and it's nothing to laugh at, but nobody has really put forth a good 7mm-08 AR10 carbine. I think they're meant for each other.
 
Found this


7mm-08 Remington

History

First experimented with by Wildcatter’s, the 7mm08 is based simply on the .308 Winchester case necked down to 7mm. The original wildcat was utilized by both hunters and target shooters, gaining greater attention in the target shooting arena. Based on popularity, Remington officially adopted the cartridge in 1980 without any changes to the wildcat name or design.

After its formal introduction sales of 7mm08 rifles were modest but in no way an immense success. It was not until the mid to late 1990’s, the beginning of the ultra lightweight rifle trend, that the 7mm08 became a focal point for both hunters and retailers. Since 2000, the 7mm08 has absolutely soared in popularity. The cartridge is often promoted by retailers as having light recoil yet high down range energies while being available in light weight rifle platforms.

The 7mm08 is also enjoyed by a newer type of western hunter, generally speaking, by those who have great work commitments and little time to hand load or practice hunting and shooting with higher recoiling rifles. The cartridge is supported by an abundant range of full pressure yet mild powered factory ammunition, ideally suited to medium game hunting.

In competition circles the 7mm08 has lost a great deal of ground to the 6.5’s. Although the 6.5 bore has the potential to produce excellent exterior ballistics combined with minimal recoil, bore selection for match shooting has been and always will be equally effected by fashion trends and subjective experience.

Performance

The 7mm08 is often promoted as having a flatter trajectory than the parent .308 while producing less recoil. Unfortunately it is easy to take the above comment out of context. Like the 7mm08, the .308 can be loaded with a range of high BC projectiles which produce desirable trajectories and both are exceptionally useful cartridges. The .308 is somewhat more flexible where a heavy bullet is needed or wanted for use on large animals. With 140 grain hunting bullets the 7mm08 is flatter shooting than the .308 loaded with 150 grain hunting bullets, showing an advantage as a lighter medium game hunting cartridge when utilizing factory loaded ammunition.

One of the greatest traps regarding the 7mm08 has been a range of lightweight rifle designs that produce often intolerable recoil, recoil similar to that of a standard weight .300 Magnum. A large number of hunters are currently ‘enduring’ the recoil of the 7mm08 without knowing that what they are experiencing is unnecessary.

Generally speaking, most current factory 140 grain 7mm08 loads achieve 2800-2840fps from 22” barrels. Killing performance tends to duplicate the 6.5x55. At close ranges, wounding on medium game is broad and kills are very fast. At ranges beyond 150 yards, as velocity falls below 2600fps, kills can be delayed. On tough animals, kills may be so slow as to allow animals to escape great distances.

At the a fore mentioned ranges beyond 150 yards and using factory 140 grain ammunition, the hunter should aim to break the foreleg bones of game. Both rear lung and neck shots from various brands of 7mm08 ammunition often result in very slow killing at extended ranges. With care to shot placement, the 7mm08 gives excellent results and like the 6.5x55, it is all too easy to become lulled into a false sense of security. It is therefore not unusual to have a string of successes followed by an abysmal failure after neglecting the above mentioned shot placement.

With many 140 grain 7mm08 factory loads, penetration is poor on tough medium game. To some extent, both the demand and expectations of the 7mm08 are so high that ammunition manufacturers are asked to produce the impossible. As a compromise, to promote fast killing at ranges of 200 to 400 yards, loads are designed to produce explosive wounding for the fastest possible kills rather than deep penetration and exit wounding on tough game. Hunters must therefore set realistic expectations of factory ammunition performance.

With hand loads, the hunter has a huge range of options and can tailor loads to suit a variety of situations. From the typical 22” barreled production sporting rifles, velocities for 140 grain loads are usually around 2800-2840fps, about 80fps slower than the 7x57 due to the difference in traditional barrel lengths. The 140 grain bullets lose velocity quickly and beyond 150 yards, the effects of various bullet designs become more pronounced.

Heavier 154-162 grain 7mm bullets often produce the most consistent results in the 7mm08 across a wide range of game body weights and ranges. The only downside of this approach is that at a theoretical level, the lower velocity of a 154-162 grain bullet seems to go against everything hunters have striven towards for the last 100 years - high velocity as a means to produce fast killing.

Each cartridge has its own performance parameters and using a slower, yet higher BC bullet in the 7mm08 does not in any way remove killing power or limit trajectory within this cartridge’s existing limitations. This
is not the same theory as the slow moving heavy bullet practice relative to big bore performance or 20th century ballistics theory. Rather, it is simply a method of utilizing current bullet designs, particularly the sleek, soft 162 grain A-max. The A-Max allows the hunter more error with shot placement at extended ranges as rear lung wounds are usually so severe that game cannot move far once hit. At the same time, velocity from the 7mm08 is so mild as to not cause shallow penetration with point blank range raking shots.

Factory Ammunition

Although Remington adopted the 7mm08 as their own, this company have produced some very poor performing 7mm08 ammunition over the past few decades. Fortunately, due to intense competition, modern loads are much more potent than before. Current loads include the 120 grain hollow point at 3000fps, the 140 grain Core-Lokt at 2860fps and the 140 grain Accutip, also at 2860fps.

Remington’s 120 grain hollow point is designed for varmint hunting but is adequate for game as heavy as 40kg (90lb). The 140 grain Core-Lokt load has a jaded history. Initial velocities for this load were very low and produced poor case neck to chamber obturation along with excessive powder fouling at the neck and throat area of rifles. The compacted powder residues raised pressures while destroying accuracy. Velocity was in the region of 2650 to 2750fps and with the extremely poor BC of .390, the Core-Lokt load did not run true to the advertised claim that the 7mm08 produced superior ballistics to the .308.

The current 140 grain Core-Lokt load achieves a velocity of around 2800fps in 22” barrels, slightly but insignificantly lower than 24” test barrel velocities. While its BC may be poor, performance on game out to moderate ranges is excellent. For hunters who seldom take shots beyond 200 yards, the Core-Lokt is inexpensive yet highly effective, producing both broad wounding and reasonably deep penetration with minimal risk of jacket core separation.

The more recently introduced 140 grain Accutip is quite different to any former Remington loadings. Remington made an effort to ensure this load achieved maximum velocities along with desirable longer range performance. The only downside is that this load is terribly expensive for U.S hunters, let alone export countries where one packet of Accutip ammunition can cost the same as a weeks groceries for a single man.

At close ranges, the Accutip (which is most likely a re-branded SST), produces immensely traumatic wounding on medium game. This is not an Elk bullet, doing its best work on all game up to weights of around 80kg (180lb). Penetration is fair at close ranges although retained bullet weights tend to be lower than 50%. At longer ranges, the Accutip can suffer jacket core separation but at such ranges (250 yards and beyond), this behavior is not usually detrimental to wounding as the bullet fragments are large and lethal. From a velocity of 2840fps, the Accutip does its best work inside 250 yards (2400fps). Beyond this range the bullet design and power of the 7mm08 limit wounding although kills are normally clean, even if delayed. Performance is reduced further at 375 yards or 2200fps.

Federal have really gotten behind the 7mm08 in recent years and now produce several useful loads. These include the 140 grain Nosler Ballistic Tip at 2800fps, the 140 grain Accubond at 2800fps, the 140 grain partition at 2800fps, the 140 grain Barnes TSX at 2820fps, the 140 grain Fusion at 2800fps and finally, the 150 grain Speer Hotcor at 2650fps. For unknown reasons, all of these loads achieve velocities faster than the above advertised specifications regardless of the fact each were developed in a 24” test barrel. From typical 22” barreled sporting rifles, Federal’s 140 grain loads achieve 2840fps while the Hotcor achieves an outstanding 2750fps. None give excessive pressure and all have the potential to produce outstanding accuracy in suitably tuned rifles.

The 140 grain Ballistic Tip is, as can be expected, a general purpose open country load. Wounding is thorough and violent at closer ranges, killing is clean but in no way spectacular. For smaller species of Whitetail and other game of this size, the BT is an ‘adequate’ performer out to ranges of 350 yards. On small but tough animals such as pigs, the BT can be quite shallow penetrating and wounding limited by the power of this cartridge. It should be noted that Nosler’s original ideal bullet design was the Partition, the Solid base and later the Ballistic Tip created to meet trends, rather than performance orientation.

The Accubond is another humble performer producing wide internal wounding and clean killing but with relatively deep penetration. Hunters should not expect exceptionally deep penetration with this bullet as it has a very low SD. As a medium game bullet, the AB is a good all-rounder.

The 140 grain 7mm Partition is much like the Accubond, both produce a wide wound regardless of the focus towards optimum controlled expansion within each design. Again, a low SD as a result of the 140 grain 7mm bullet weight dictates that for best performance, the Partition and Accubond do their best work on game weighing up to 80kg (180lb). Both bullets are adequate for game up to 150kg (330lb) but this weight should be considered a maximum. The Accubond and Partition often produce surprisingly good performance at lower velocities of 2200fps or 300-350 yards providing game are not too lean.

The stoutest bullets in the Federal line of ammunition are the 140 grain Barnes TSX and the 140 grain Fusion loading. The Fusion bullet is a very odd, almost rushed design. At close ranges upon impact, the Fusion will often fail to impart any measure of hydrostatic shock and game can appear quite unaffected by well placed shots. After impact on medium game, the bullet expands, produces a quite normal wound channel (similar to other 7mm 140 grain bullets) while gradually breaking down until very little is left of the original projectile. The broken off fragments tend to be small, often less than 1mm (40 thou) in diameter. To this end, the Fusion is neither a fast killing or deep penetrating projectile.

The 140 grain TSX is undoubtedly a deep penetrating projectile, able to take a 1200lb animal broadside, although, such a practice should be considered unethical due to the small diameter of the wound. Nevertheless, this bullet is the best choice in the 7mm08 for tough game weighing between 90 and 320kg (200-700lb).

On lighter medium game, the TSX is a little too stout for all round work. This does not mean that the Barnes does not readily expand, to the contrary, wounding through vitals is ideal. The only problem with using this projectile on lighter game is that the trauma does not also occur immediately upon impact or during exit wounding. Kills at impact velocities below 2600fps and especially below 2400fps can be very slow as a result. If the TSX is to be used on lighter medium game, bullets should be placed to break major bones and locomotive muscles in order to effect immediate incapacitation.

Federal’s heavy weight load for the 7mm08 utilizes a proprietary 150 grain Speer Hotcor bullet with a cannelure, a design feature which is not normally available to hand loaders. This is one very good medium game loading. The Speer opens up quickly on impact, produces a wide wound channel before expansion is arrested by the cannelure. Penetration is slightly better than the Fusion load which costs twice the price of the budget branded Hotcor loading and is on par with the Partition and Accubond loads.

Winchester produce two loads for the 7mm08, the 140 grain Power Point at 2800fps and the 140 grain Ballistic Silvertip at 2770fps. Both are humble performers offering rapid expansion but limited penetration.

Hornady currently list two Superformance loads. These include the 139 grain SST at 2950fps and the 139 grain GMX at 2910fps. Like the former Light Magnum loadings, the Superformance ammunition gives ‘true to advertised’ velocities in 24” barrels. As is almost always the case, shorter barrels lose 35fps per inch of barrel removed. In standard 22” sporter barrels, the SST at 2890 is slightly faster than Federal loads and also slightly faster than can normally be achieved with hand loads.

The 139 grain SST is very hard hitting out to 250 yards (2400fps), producing a wide, violent wound. Penetration is reasonably good at impact velocities above 2600fps (150 yards) due to the swaging/forming of a uniform mushroom, although the 139 grain SST is unsuitable for tail on shots on light bodied game. At longer ranges, the 7mm 139 grain SST projectile is prone to suffer jacket core separation however cross body and quartering wounding is usually more than adequate. The GMX is, like the Barnes TSX, better suited to heavier animals above 90kg (200lb) as opposed to all round use, simply because on light game, even though wounding can be broad, the delay in killing can lead to difficulty tracking dead run game.

Reloaders logo.jpg

Hand Loading

The 7mm08 is often compared with the original 7x57 with regard to which is the more potent of these two mid powered cartridges. Some hunters have posed the question - “was there any need for the 7mm08?” The 7x57 certainly has a longer case with a longer neck than the 7mm08. Rifles chambered in 7x57 also have a longer free bore and longer magazines than the 7mm08, adding versatility when using 160 to 180 grain bullets. Having said this, the 7mm08 utilizes the minimal body taper and over all efficiency of the parent .308 Winchester cartridge. To this end, variations in individual rifles close the gaps between the 7mm08 and 7x57 considerably and it is not uncommon for 22" barreled 7mm08 rifles to duplicate various 24” barreled 7x57 rifles as can happen vice versa. If one were to really push the point, the .284 Winchester is more powerful than either and more the underdog if there is to be a prize for the most deserving of acclaim.

The 7mm08 gives best results with the same powders used in the 7x57, Varget (ADI 2208) works best with 120 to 140 grain bullets while the 4350 burn rate powders work well with heavier bullets or long barrels Realistic velocities from a 22" sporter are 3050fps with 120 grain bullets, 2850fps with 140 grain bullets, between 2750fps with 150 grain bullets, 2650fps with 160-162 grain bullets, 2550-2600fps with the 168 grain Berger VLD and 2450fps with 175-180 grain bullets.

One interesting factor is that all Federal factory loads achieve higher velocities from 22” sporting barrels, than the velocities achieved in various reloading manuals. As always, experimentation is the key towards developing high velocity combined with acceptable pressure and excellent accuracy.

Competition shooters generally adopt barrel lengths of up to 32” for the 7mm08. With slow burning powders, velocity gains between 22” and 28” are generally 35fps for a cartridge of this capacity. Long range hunters will also sometimes adopt long barreled rifles chambered in 7mm08 and in doing so, recoil is reduced to extremely low levels.

Due to the fact that the 7mm08 and 7x57 are so similar in potential velocities, all reloading component bullet performance has been discussed in the 7x57 text. To recap; the 120 grain bullet weight is best suited to the lightest of game species (under 40gk/70lb) due to limited penetration. Most 139/140 grain 7mm bullets produce good, but not outstanding performance. Of the current 140 grain bullet designs, the 140 grain Hornady SST is the most dramatic killer on lighter weight medium game, the Hornady InterBond and Nosler Accubond have high BC’s, but give deeper penetration than the SST and can be slightly more effective on medium sized yet tough game.

The 150 to 154 grain bullet weight can be very effective in the 7mm08 when used on game weighing around 90kg (200lb) out to moderate ranges. The 150 grain Nosler Partition is an excellent medium game killer. For those wanting higher down range energies via high BC’s, the 154 grain SST/InterBond combination work extremely well together, the SST performing better at impact velocities of between 2600fps to 2200fps, the InterBond performing well at woods ranges. The 154 grain SST is somewhat unique in its ability to produce wide wounding if major bones are struck at impact velocities below 1800fps however it can be difficult to ensure a bone strike in higher winds at long ranges.

The 160-162 grain bullet weight is very useful in the 7mm08 providing bullet construction is matched to game weights. The 162 grain Hornady A-max is an immensely useful all round bullet, performing well at both close and long ranges on light to medium weight game. Tougher projectiles like the outstanding 160 grain Nosler Partition and Accubond projectiles do their best work on large medium game such as Elk, at close to moderate ranges.

For tough game weighing between 150 (330lb) and 320kg (700lb), the 140 and 150 grain Barnes TSX projectiles produce an excellent combination of broad wounding versus deep penetration in the mild sevens. The 160 and 175 grain Barnes TSX projectiles produce exceptionally deep penetration but limited wounding potential at 7mm08 velocities and are best suited to the largest of game, above 450kg (1000lb). The 7mm08 and 7x57 are not particularly well suited to use on large, heavy game due to narrow chest vital wounding, regardless of deep penetration. For this reason, even if using a tough bullet like the TSX or monolithic solid, neck or head shots on large game are always the most humane method of killing.

Closing Comments

The 7mm08 has seen an immense rise in popularity, beginning with the trend towards ultra light rifles in the mid to late 1990’s, growing further with the collapse of the U.S property market in 2006, marking the beginning of the Global recession of 2007-2010. Although the 7mmWSM could have knocked the 7mm08 off the market a long time ago, factory ammunition for the 7mm08 has been much cheaper to obtain during the recent world wide financial troubles. The problem of ammunition costing was also compounded by China’s demand for raw materials, causing a dramatic rise in metal costs from 2005 onwards.

As for the light weight rifle trend, the 7mm08 was for some time the most preferred light weight high power rifle chambering for hunters that climbed to the highest, most dangerous peaks in search of alpine game. Today, the larger magnums are becoming more acceptable to such hunters due to advances in technology such as ballistics software, enabling longer range shooting. Nevertheless, the 7mm08 retains a number of fans, many having hunted with this cartridge for most of their hunting careers. The 7mm08 is a cartridge that serves both youths and adults well, is mild to shoot in suitable platforms and is ideal for a vast range of applications.

Suggested loads: 7mm 08 Barrel length: 22”
No ID Sectional Density Ballistic Coefficient Observed MV Fps ME
Ft-lb’s
1 FL Fed 140gr Accubond .248 .485 2800 2437
2 FL Fed 150gr Hotcor .266 .413 2750 2518

Suggested sight settings and bullet paths
1 Yards 100 150 252 292 325 350 375 400
Bt. path +3 +3.5 0 -3 -6.5 -9.5 -13 -17
2 Yards 100 125 242 280 325 350 375 400
Bt. path +3 +3.4 0 -3 -8 -11.5 -15.5 -20


No At yards 10mphXwind Velocity Ft-lb’s
1 300 6.4 2260 1587
2 300 7.9 2129 1509
 
just ordered a 26 inch Shilein 1-9 twist CM Blank, I will parkerize it when finished.
I have everything else except the reamer which i will rent when the barrel gets here.

if it turns out like I want I will make another with the Bartlin SS barrel, this will be my first AR10 Style barrel make so I did not want to scrap a 340.00 Blank on the first try.
 
should be fun.... once I get a load up 140 to 162 bullets, I may opt for a 1-8 twist barrel, but we will see how this 1-9 works.
I will have the barrel in a few days and will toss it on the lather over thanks giving break...
 
The 154 SST has a G1 BC of .530 as well. I think a 16" could push that at 2600fps, since a 24" pushes it up to 2800fps with RL17.

A prone gun will be boring: too heavy, sits on a bipod, can't shoot positions, can't really stalk hunt with it, etc.

A Designated Marksman Carbine can be used to shoot people in the face in the house, then reach out to 1000yds plus, then taken hunting. If you cut to 16" or 17", you will have another section of blank available for an SBR or TC to sell.

This is with the 154gr SST at 2600fps
Code:
       Range    Velocity    Energy     Trajectory         TOF          Drift
      (yards)     (fps)     (ft-lb)       (MILS)         (sec)         (MILS)
          0      2600        2311           0.00         0.0000         0.00
         50      2515        2164          -0.37         0.0586        -0.09
        100      2433        2023           0.00         0.1193        -0.19
        150      2351        1890          -0.15         0.1820        -0.29
        200      2272        1764          -0.44         0.2469        -0.40
        250      2193        1645          -0.80         0.3141        -0.50
        300      2117        1532          -1.21         0.3837        -0.61
        350      2042        1425          -1.66         0.4558        -0.73
        400      1968        1325          -2.14         0.5307        -0.85
        450      1896        1230          -2.65         0.6083        -0.97
        500      1826        1140          -3.19         0.6889        -1.10
        550      1758        1057          -3.77         0.7726        -1.23
        600      1692         978          -4.38         0.8596        -1.36
        650      1627         905          -5.03         0.9500        -1.51
        700      1565         837          -5.71         1.0440        -1.65
        750      1505         775          -6.44         1.1417        -1.80
        800      1448         717          -7.20         1.2434        -1.96
        850      1393         663          -8.02         1.3490        -2.12
        900      1341         615          -8.88         1.4588        -2.29
        950      1292         571          -9.79         1.5728        -2.45
       1000      1247         532         -10.75         1.6910        -2.63
 
I do love the 7mm-08 but there is another 7mm id run in an ar-10. Mark from SAC has developed a 7mm creedmore. This would give you a shorter OAL with almost identical ballistics. This would be a huge advantage and allow you to test with the 162s set out to give you much more case capacity. Just an idea.

Good luck,
Merritt
 
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This is something I have begun researching myself for my LMT LM8. My primary bolt gun is a 27" 7-08, and would love the ballistics of that round in a 16-18" gas gun. Once I can do some more research on how the round may perform out of short barrels, I will begin the search for someone to make me a 7mm LMT barrel.
 
How does less case volume equal more case capacity? You can load the 162gr A-MAX to 2.800" in the 7mm-08, with a case that has the same shoulder geometry as the .308, which the AR10 mags and feed ramps are meant for.

I've seen this argument with the 6.5 Creedmoor vs. the .260 Remington, and it has no merit in the AR10 as well as a bolt gun. The only advantage I see is the shoulder angle of the Creedmoor, which supports a more efficient burn.
 
well all ordered and on its way
I have a 26 inch Blank coming and a 20 inch blank coming, I have decided to build both and see what is what.... braking the bank here :p
So lets start with a 17 inch barrel and see how it performs, then cut to 16 inch if needed
 
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I am looking to build an AR in 7mm 08 and am keeping an eye on your progress.
I can't wait to see how your build turns out.
 
How does less case volume equal more case capacity? You can load the 162gr A-MAX to 2.800" in the 7mm-08, with a case that has the same shoulder geometry as the .308, which the AR10 mags and feed ramps are meant for.

I've seen this argument with the 6.5 Creedmoor vs. the .260 Remington, and it has no merit in the AR10 as well as a bolt gun. The only advantage I see is the shoulder angle of the Creedmoor, which supports a more efficient burn.

Its because you are limited to how far you can neck out the higher BC bullets to meet the lands when you are locked into a semi auto magazine fed OAL. For instance my bolt gun with a 7-08 I was necked out to 2.910 oal. I needed that length when running the 162s to get close to the lands. If you oal is limited to 2.800 then your bullet is seated deaper into the case. However with a creedmore case the bullet can be necked out more because the case length is shorter. Essentially putting more of the powder behind the bullet and making it a much more efficent cartridge.

Good luck,
Merritt
 
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The Remington R25 comes in 7-08. There were even some M1As made for the European market where .308 is forbidden.

"Ex Umbris Venimus"
 
I built this 7-08 on a Mega MATEN platform in 2011.



I had PT&G optimize the reamer for 162 A-Max using re-sized 308 brass. The barrel is a heavy profile Lilja SS blank 1:8 twist, 22" long. I used a JP Lo-Mass bolt carrier and their enhanced bolt.

I like the rifle but it was my first build and there is some things that I would do differently if I did it again. And I wish I would have seen this thread a when you first posted it because you are more than welcome to use my reamer.

Your project sounds like a winner. If you want to know some things I learned building mine I'd be happy to share them.
 
I built this 7-08 on a Mega MATEN platform in 2011.



I had PT&G optimize the reamer for 162 A-Max using re-sized 308 brass. The barrel is a heavy profile Lilja SS blank 1:8 twist, 22" long. I used a JP Lo-Mass bolt carrier and their enhanced bolt.

I like the rifle but it was my first build and there is some things that I would do differently if I did it again. And I wish I would have seen this thread a when you first posted it because you are more than welcome to use my reamer.

Your project sounds like a winner. If you want to know some things I learned building mine I'd be happy to share them.

Share away i just decided today to build my MKM into a 7-08 22" barrel
 
I think 7mm-08 is what the .308 should have been, although I would be more interested in what you could do with a lightweight DM Carbine project.

Looking at the 162gr pills, you would crush the 175gr .308 SMK. The 162gr A-MAX has a BC of .625 G1! The 162gr SST is .540...

A really cool challenge for a smith would be to see how well you could lighten the receivers, lighten the barrel profile without ruining accuracy, and what the optimum barrel length and gun balance is for a long-range capable, DMC based on the T65 case in 7mm. Do you already have receivers and BCG? This is what I'm referring to:



We already know what a 22" to 24" 7-08 will do, and it's nothing to laugh at, but nobody has really put forth a good 7mm-08 AR10 carbine. I think they're meant for each other.



That KAC SR-25 is f$*$king sweet.
 
what accuracy were you getting

I get decent accuracy, 1 MOA, but not bug holes. What I wish I got more of was velocity. I'll have to go review my load notes to say for sure but I never got much better than the starting load velocity for the 162 A-Max before I got flattened primers. This was handloading with Alliant PP200MR, H-4350 and 8208 XBR. I think this was caused by a couple of things: Being limited to 2.800" max OAL with the 162 A-max limits your case capacity. And, my chamber has a relatively short throat. Dave Kiff at PT&G recommended the chamber dimensions though so I cant really argue that point. With the short throat, I think I would get better ballistics from a lighter bullet even though the BC would be worse than the 162gr. And, the JP Lo-Mass bolt carrier is not a good fit for this caliber. Especially if you are trying to wring out every available fps from a heavy bullet. I had to add mass to the bolt carrier to make it function reliably and also really pinch back on the gas. I think I can recommend to you that you use a standard weight bolt carrier and an adjustable gas block. And you might consider a long-ish throated chamber too.

I got the following load data from the Hodgdon website. It is for 7mm-08 Remington. I copied the load data for 162gr and 160gr bullets using IMR-8208 XBR powder. At first glance the velocities for the 162gr bullet look pretty good but look at the COL; 2.875" All the 162gr loads are for this COL but we know that we are limited to 2.800" COL by the magazine. The closest bullet weight to 162gr listed on the Hodgdon website with a max OAL of 2.800" is 160gr. Its almost 200fps slower in the shorter loading. These are the velocities I think you can expect from the 7mm-08 in the AR-10 platform with the 162gr load. They match pretty well with my results.

162 GR. HDY A-MAX IMR IMR 8208 XBR .284" 2.875" 36.2 2499 41,000 CUP 40.2 2725 50,800 CUP

160 GR. SPR SPBT IMR IMR 8208 XBR .284" 2.800" 35.5 2459 45,400 CUP 37.7 2554 49,900 CUP
 
Flat primers usually mean nothing in a gas gun. The amount of headspace slop necessary for them to chamber reliably means that rearward movement is a given, and the primer moves first.

It also helps to cut your chamber for the type of bullets you're shooting. In my last case, I had GA Precision cut my throat for the 139gr Scenar in my .260 Remington, knowing what magazines I'm feeding from. As a result, not only the Scenars, but the Berger 130gr VLD's shoot superbly from my gun at 2.810" COL.

There are metal mags that will allow more COL than the PMAGs, or you can modify PMAGs to allow more COL inside the front.

Gas port diameter is going to be a big factor, and I prefer a straight port over a choked one because of erosion. Adjustable gas blocks form a chamber that torches your gas port, leading to earlier erosion, and consequential accuracy loss. It's better to start with a smaller port, then open it if you need to, than to choke it off.

Another modification would be to bush the firing pin on the DPMS .080" pin hole diameter, which is a limiting factor in higher pressure loads.
 
How many calibers does GAP offer ? I like reading about all these diff calibers in semi-autos as I was a wildcat buff many yrs ago, but only with single shot rifles and handguns. Anxious to see your project develop.
 
Flat primers usually mean nothing in a gas gun. The amount of headspace slop necessary for them to chamber reliably means that rearward movement is a given, and the primer moves first.

It also helps to cut your chamber for the type of bullets you're shooting. In my last case, I had GA Precision cut my throat for the 139gr Scenar in my .260 Remington, knowing what magazines I'm feeding from. As a result, not only the Scenars, but the Berger 130gr VLD's shoot superbly from my gun at 2.810" COL.

There are metal mags that will allow more COL than the PMAGs, or you can modify PMAGs to allow more COL inside the front.

Gas port diameter is going to be a big factor, and I prefer a straight port over a choked one because of erosion. Adjustable gas blocks form a chamber that torches your gas port, leading to earlier erosion, and consequential accuracy loss. It's better to start with a smaller port, then open it if you need to, than to choke it off.

Another modification would be to bush the firing pin on the DPMS .080" pin hole diameter, which is a limiting factor in higher pressure loads.

Just to clarify, I told Dave Kiff at PT&G that I wanted a reamer optimized to shoot the 7mm 162gr Hornady A-Max from a semi-auto platform. So the chamber should be compatible if not optimal for the A-Max.
 
What a cool project! If the accuracy is there, I could see trading my R700 7mm-08 & my AR15 300blk for an AR-10 in 7mm-08.
 
Did you find any brass? I bought a lot of 7mm-08 brass made by Winchester when I started with the .260 Remington, and it's excellent brass.

Looking forward to how this project turns out.
 
I get decent accuracy, 1 MOA, but not bug holes. What I wish I got more of was velocity. I'll have to go review my load notes to say for sure but I never got much better than the starting load velocity for the 162 A-Max before I got flattened primers. This was handloading with Alliant PP200MR, H-4350 and 8208 XBR. I think this was caused by a couple of things: Being limited to 2.800" max OAL with the 162 A-max limits your case capacity. And, my chamber has a relatively short throat. Dave Kiff at PT&G recommended the chamber dimensions though so I cant really argue that point. With the short throat, I think I would get better ballistics from a lighter bullet even though the BC would be worse than the 162gr. And, the JP Lo-Mass bolt carrier is not a good fit for this caliber. Especially if you are trying to wring out every available fps from a heavy bullet. I had to add mass to the bolt carrier to make it function reliably and also really pinch back on the gas. I think I can recommend to you that you use a standard weight bolt carrier and an adjustable gas block. And you might consider a long-ish throated chamber too.

I got the following load data from the Hodgdon website. It is for 7mm-08 Remington. I copied the load data for 162gr and 160gr bullets using IMR-8208 XBR powder. At first glance the velocities for the 162gr bullet look pretty good but look at the COL; 2.875" All the 162gr loads are for this COL but we know that we are limited to 2.800" COL by the magazine. The closest bullet weight to 162gr listed on the Hodgdon website with a max OAL of 2.800" is 160gr. Its almost 200fps slower in the shorter loading. These are the velocities I think you can expect from the 7mm-08 in the AR-10 platform with the 162gr load. They match pretty well with my results.

162 GR. HDY A-MAX IMR IMR 8208 XBR .284" 2.875" 36.2 2499 41,000 CUP 40.2 2725 50,800 CUP

160 GR. SPR SPBT IMR IMR 8208 XBR .284" 2.800" 35.5 2459 45,400 CUP 37.7 2554 49,900 CUP

Try RE17, it is a little slower. I shot a .18" group at 100yds using 44gr RE17 with the 140gr TSX. I didn't shoot 162s but 17 seemed to work better with the 140s than anything in the range of Varget, 15 or 8208.
 
fired test rounds today, everything worked great accuracy with the factory Honandy 139 SST sucked but function was perfect, no over pressure signs, no FTF

getting ready to Finnish the 1-10 twist 17 inch barrel and tread it for flash hider

 
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Why would .308 be forbidden?

I am aware of three European countries that ban military cartridges for certain, if not all, types of civilian firearms. They all have had problems with domestic terrorist groups. I think the ban is an attempt to make it harder for the terrorists to get ammunition for their weapons.
 
Looking forward to seeing how the 17" turns out daddy. What gas port diameter will you start with?

Sure would be nice with the KAC receiver set. They actually are available, but price is $1899. Yikes!
 
yep I remember, when the subs grounded as well, camp greaves was a pain to be stationed at during those times 91-92
this is one of my favorite rifles other then my Scar17


stands alone!!!
 
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I loved Camp Greaves...far away from all the Army BS down at Camp Casey, with North Korea to your front, the river to your rear, and land mines to your left and right.




Currahee!