DPMS 308 LR AT 1000 yards

A

AZ.Elk.Hunter

Private
Minuteman
Jul 17, 2011
10
0
52
Arizona
#1
I am new to this site and apologize if this question has already been covered but I searched and could not find any related topics.
I recently acquired a DPMS 308 LR and have been working on a load for 1000 yards. Currently using a 165 Match King which is dead accurate out to 800. Push to 1000 and the POI is inconsistent. I have ran the drill to eliminate all human and mechanical error. I am down to the thought that it is going subsonic shortly after 800 (890 to be exact) and after that the math is out the window. Looking around many are using a 155 grain and pushing it to remain supersonic out to 12-1300 yards. The other school of thought is a 175 grain that is more forgiving in the wind.
Current pushing the round at 2540fps. Originally had it at 2725fps but by the third shot the casing showed signs of a bit too much back pressure.
We have never loaded for a semi auto and would like to save some money by not wasting it on loads that will not accomplish the goal.
Any suggestions based on experience?
 
#3
Re: DPMS 308 LR AT 1000 yards

24 inch barrel. With all of my bolt action rifles the heavier round has made all the difference. My concern with a 175 on this rig is bolt integrity. I have no experience developing a load for a semi auto and this is my first DPMS. I have no intent on rapid firing but still wonder how the bolt will hold up. Not arguing, more speaking my thoughts and asking for advise.
 
#4
Re: DPMS 308 LR AT 1000 yards

Forgot to add, I am not a competition shooter. I am satisfied with hitting the bread box on a deer or pronghorn at 1000 yards. With that in mind, what do you consider "good enough". For me, it is hitting a 17" X 14" target cold bore.
 
#6
Re: DPMS 308 LR AT 1000 yards

Depending on your altitude and temp, you may be going subsonic or close to it @ 1K with your current load. Some bullets don't make the transition well, as you mentioned a solution would be 155s and push em hard or go with the 175s and push em hard, the 155 Lapua Scenars are hard to beat. You may want to play around with a few different powders as well, I run RL15 in all the AR10s pushing either 155s or 175s.

Kirk R
 
#7
Re: DPMS 308 LR AT 1000 yards

Interesting, I never considered the effect of a round going subsonic just short of my target. I assumed the flight path would remain until altered by the environment. That would explain my confusion as to why at 800 I can punch the same hole twice and at 1000 I am all over the map. I could not accept that 1-200 yard later the wind has pushed it all over creation and back.
 
#11
Re: DPMS 308 LR AT 1000 yards

Hello I knoe this isn't your ansewr to your question but I am looking onto getting and AR also I was going to use the 308 becuase thats what I used in the military...but after alot of reading I am leaning toward the 260 in the ar I was wondering why you chosse the 308...
 
#12
Re: DPMS 308 LR AT 1000 yards

On average that SMK 168 at sea level is going subsonic just after 800 yds. I shot a 1/2 MOA group at sea level one time with Fed GMM 168 ammo then at 900 yds it was 1 MOA then at 1000 yds it was keyholing through the target. Great bullet to 800 yds but after it runs out of steam and gets nasty.

I've shot the 155 Scenars and pushed them real hard and they perform well out to 1000 yds (using Varget) but they are pricey.

Try that 175 SMK (not as costly) and with that BC you'll get to 1000 yds no problem. I use IMR4895 (anywhere from 40.0 to 42.5 grains) not a cutting edge powder but proven and works well in a bolt or gas gun (I can use it for .223 & .308 is why I like it).

Not a worry on the bolt - it'll take it.
 
#13
Re: DPMS 308 LR AT 1000 yards

I second BCP's suggestion.

Benchmark is far too quick burning with heavy 308s. Try Alliant's 2000MR powder, Varget, Reloader 15, or BLC(2). The last two powders are temperature sensitive.

Give it a whirl and report back.

I also noticed in your post you backed off from 2700+ fps to 2540. That is a huge step back in powder charge...what you want to do is work up slowly in 0.2gr - 0.5gr increments until u start noticing high pressure signs, then back off about 0.5grains or more to the highest accuracy node within safe pressure limits.

Regards,
 
#14
Re: DPMS 308 LR AT 1000 yards

I'm not sure how the 155's would do from a gas gun, they need a good amount of velocity to perform well at distance and you lose a lot with the gas system. Also my experience is that scenars don't like to jump to the lands so you would run into mag length issues. For a gas gun the 175 class bullets seem like the best bet.
 
#15
Re: DPMS 308 LR AT 1000 yards

On the DPMS 308 I recommend you get an Xtra Heavy buffer and an Armalite AR10 recoil spring. I got these parts from Slash on arfcom. This will allow better brass life with reloads.
 
#16
Re: DPMS 308 LR AT 1000 yards

I shot my 178amax load easily out to 1100 today. I didnt hit the target because I was 8moa over my dope
frown.gif


Made several hits on the 900 and 1000 targets.
 
#17
Re: DPMS 308 LR AT 1000 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dieselten</div><div class="ubbcode-body">On the DPMS 308 I recommend you get an Xtra Heavy buffer and an Armalite AR10 recoil spring. I got these parts from Slash on arfcom. This will allow better brass life with reloads. </div></div>

I would skip that and just buy an adjustable gas block (that's what i did 2 times)
 
#18
Re: DPMS 308 LR AT 1000 yards

The load on the bolt will be proportional to the case pressure.
The weight of the projectile has no effect on the bolt thrust.
The lower velocity of the heavier bullet gives that force acting on the bolt a longer duration, making it "feel" harder on the bolt.

Bullets going transonic can do so very predictably, if they remain stable.
If you see elongated holes in the target (ice cream cone shaped), that tells you that they were unstable.

When bullets become unstable they will begin to wobble with the bullet tip hunting around in a circular arc.
It will eventually develop into to a full key-hole where the bullet rotates through the air like a propeller would.

If you don't see this evidence at the target, then it isn't happening.
If you have say: a 1:12 twist with 168's, you will most likely experience this near the sound barrier where dynamic pressure is high.

The important variables are: twist rate, bullet velocity, and bullet length (excluding atmosphere).
Bullet weight only indirectly affects stability because it lowers the velocity, and thus the amount of spin the bullet receives.
It also is usually longer as well.

A 1:10 twist with 155's.......I've never had a stability issue, even at very low density altitudes (high air density).
My 18.5" barreled ar10 will go 1000 yards, supersonic, even at around 0 deg F. at 800 ft. alt.
My load: 1:10 twist, with 155 SMK's, 46.5 Varget. (>2700 fps)
I've gone up to 48.0 and pressure was acceptable for me.
Accuracy wasn't as good.

If you are getting lateral POI variations, you may be seeing some stability issues.
Measure your twist rate with a cleaning rod.
If the (168 SMK?) isn't stable, go with a 155.

There really isn't any gas-gun voodoo.
Don't waste time on buffers and springs unless the rifle isn't operating correctly, and even then there is likely more to the story that those parts won't fix anyhow.


 
#20
Re: DPMS 308 LR AT 1000 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RunsWithScissors</div><div class="ubbcode-body">On average that SMK 168 at sea level is going subsonic just after 800 yds. I shot a 1/2 MOA group at sea level one time with Fed GMM 168 ammo then at 900 yds it was 1 MOA then at 1000 yds it was keyholing through the target. Great bullet to 800 yds but after it runs out of steam and gets nasty.

I've shot the 155 Scenars and pushed them real hard and they perform well out to 1000 yds (using Varget) but they are pricey.

Try that 175 SMK (not as costly) and with that BC you'll get to 1000 yds no problem. I use IMR4895 (anywhere from 40.0 to 42.5 grains) not a cutting edge powder but proven and works well in a bolt or gas gun (I can use it for .223 & .308 is why I like it).

Not a worry on the bolt - it'll take it. </div></div>

I'll second that IMR4895 data with the 175gr. I run 42gr in a 18" and it will get there.
 
#23
Re: DPMS 308 LR AT 1000 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tx_Flyboy</div><div class="ubbcode-body">dieselten,

Mr Slash peddles that nonsense to the fan boys at Arfcom so he can sell them his $100 buffers that are "better". </div></div>

I disagree.

The factory DPMS 308 guns are way over gassed. This beats the hell out of the guns and brass and causes the bolt to open earlier.

Think about it, the rifle functions perfectly with a buffer that weighs twice as much and with a spring with double the tension. How could the original as issued rifle possibly be set up correctly?

There is a recent thread in this forum from a gunsmith trying to set up an adjustable gas block on a DPMS 308 and he had to set it at 1/4 turn from full closed.

Just because Slash sells this stuff on arfcom, doesn't mean it don't work.
 
#24
Re: DPMS 308 LR AT 1000 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dieselten</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tx_Flyboy</div><div class="ubbcode-body">dieselten,

Mr Slash peddles that nonsense to the fan boys at Arfcom so he can sell them his $100 buffers that are "better". </div></div>

I disagree.

The factory DPMS 308 guns are way over gassed. This beats the hell out of the guns and brass and causes the bolt to open earlier.

Think about it, the rifle functions perfectly with a buffer that weighs twice as much and with a spring with double the tension. How could the original as issued rifle possibly be set up correctly?

There is a recent thread in this forum from a gunsmith trying to set up an adjustable gas block on a DPMS 308 and he had to set it at 1/4 turn from full closed.

Just because Slash sells this stuff on arfcom, doesn't mean it don't work.
</div></div>
Because what you are saying isn't true.
The Slash recoil spring is NOT twice the spring rate.

Bolt carrier + buffer + firing pin = total reciprocating mass.
The total reciprocating mass is only increased a small amount with his heavy buffers.

If you were to actually double the reciprocating mass, you would reduce the cycle energy by 1/2.
If you have a descent handle on physics, I'll elaborate.
A recoil spring with twice the spring rate would require twice the kinetic energy to cycle the same as the original.

If what you are saying was true then these AR10's are getting more than 2 times the cycle energy that they need, which they are not.

The buffer gives a place for the spring to compress, prevents the carrier key from impacting the charging handle, eases the impact of the reciprocating mass with the rear of the buffer tube, augments the total reciprocating weight, and probably it's most important function: acts as a dead-blow hammer to prevent bolt carrier bounce.
(That's why those weights within the buffer have a little room to flop around).

The carrier should achieve a velocity of around 21 ft/sec, accelerates over a distance of about 0.10" (depending on reciprocating mass), and this all happens in < 0.5 milisec depending on barrel length, and gas port location.
Free travel = 0.125"
Camming distance = 0.125"
Extraction begins at about 0.25"

Rotating the bolt, while the bolt is under pressure can cause all kinds of issues.
The AR series of rifles operate dead nuts on the minimum margins required.

When I run the numbers for a 3oz. heavier buffer, I don't see a big change in the performance anywhere.
However if the bolt carrier had just 0.1" more free travel built into it's camming slot, one could see over 50% more dwell time before camming begins, and all this buffer shit would disappear.

It is hard to get away with 0.100" but half that is surely there, and it would make more difference than any buffer.

My rifles run great with the stock bolt carrier and spring.
My brass comes out looking like a bolt guns, with a little ejector swipe.
If you want to know if your rifle is over gassed, measure the gas port and compare it to the standard for that caliber/gas port location/barrel length.
 
#25
Re: DPMS 308 LR AT 1000 yards

Thank you Hamilton.

I was too lazy to type up a detailed response.

I lost interest in responding to dieselten's post when i read the blanket statement that "the factory DPMS gas guns are way overgassed".

My DPMS rifles certainly aren't,and run reliably with the stock buffer/buffer spring set-up.

Besides, IF i had an overgassed rifle, the proper fix would be an adjustable gas block to regulate the gases reciprocating the BCG/buffer/buffer spring mass. Not some overhyped buffer that sells for $100...after you spend more money to change out your buffer tube & spring to AR-10 type.

Just think FAL, and other Older rifles designed to fire a wide range of ammo of varying powder charge...the only way to accommodate such a flexibility is to have an oversized gas port that is designed around for the weakest ammo likely to be encountered, and then build in a method of regulating reciprocating the gas flow via...u guessed it an adjustable gas block.

I will say that slash's buffers do look shiny...

Regards,
 
#26
Re: DPMS 308 LR AT 1000 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dieselten</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tx_Flyboy</div><div class="ubbcode-body">dieselten,

Mr Slash peddles that nonsense to the fan boys at Arfcom so he can sell them his $100 buffers that are "better". </div></div>

I disagree.

The factory DPMS 308 guns are way over gassed. This beats the hell out of the guns and brass and causes the bolt to open earlier.

Think about it, the rifle functions perfectly with a buffer that weighs twice as much and with a spring with double the tension. How could the original as issued rifle possibly be set up correctly?

There is a recent thread in this forum from a gunsmith trying to set up an adjustable gas block on a DPMS 308 and he had to set it at 1/4 turn from full closed.

Just because Slash sells this stuff on arfcom, doesn't mean it don't work.
</div></div>
Because what you are saying isn't true.
The Slash recoil spring is NOT twice the spring rate.

Bolt carrier + buffer + firing pin = total reciprocating mass.
The total reciprocating mass is only increased a small amount with his heavy buffers.

If you were to actually double the reciprocating mass, you would reduce the cycle energy by 1/2.
If you have a descent handle on physics, I'll elaborate.
A recoil spring with twice the spring rate would require twice the kinetic energy to cycle the same as the original.

If what you are saying was true then these AR10's are getting more than 2 times the cycle energy that they need, which they are not.

The buffer gives a place for the spring to compress, prevents the carrier key from impacting the charging handle, eases the impact of the reciprocating mass with the rear of the buffer tube, augments the total reciprocating weight, and probably it's most important function: acts as a dead-blow hammer to prevent bolt carrier bounce.
(That's why those weights within the buffer have a little room to flop around).

The carrier should achieve a velocity of around 21 ft/sec, accelerates over a distance of about 0.10" (depending on reciprocating mass), and this all happens in < 0.5 milisec depending on barrel length, and gas port location.
Free travel = 0.125"
Camming distance = 0.125"
Extraction begins at about 0.25"

Rotating the bolt, while the bolt is under pressure can cause all kinds of issues.
The AR series of rifles operate dead nuts on the minimum margins required.

When I run the numbers for a 3oz. heavier buffer, I don't see a big change in the performance anywhere.
However if the bolt carrier had just 0.1" more free travel built into it's camming slot, one could see over 50% more dwell time before camming begins, and all this buffer shit would disappear.

It is hard to get away with 0.100" but half that is surely there, and it would make more difference than any buffer.

My rifles run great with the stock bolt carrier and spring.
My brass comes out looking like a bolt guns, with a little ejector swipe.
If you want to know if your rifle is over gassed, measure the gas port and compare it to the standard for that caliber/gas port location/barrel length. </div></div>

your handle on the subject seems fine to me, except that my slash buffer weighs 6.1 ounces and the stock buffer from my DPMS AP4 weighed 3.4 ounces. So It is not exactly twice the weight...my bad. And I have no way to quantify the actual spring rate but the Armalite spring is so much heavier I thought the rifle was frozen the first time I tried to charge it. It is longer also, the rifle will barely engage the bolt hold open, but it has never failed to.

How do you address the other thread I referred to, where the gunsmith had to close the adjustable gas block on an otherwise unaltered DPMS 308 and it ran correctly at 1/4 turn open? This is not right.

I stand by my statement that these guns are way over gassed.

TX flyboy - just cause your rifle functions fine and never jams does not mean it is operating optimally. Go ahead and live in denial.
 
#27
Re: DPMS 308 LR AT 1000 yards

To the OP, sorry for the thread drift...you've gotten a lot of solid reloading advise thus far...put some in practice and report back.

Dieselten,

I'm not taken to pissing contests. Hamilton gave you a scientific response...I tried to give you a real world examples of how over-gassed rifles are managed...you've ignored both of our advice.

I'm sorry if i pissed on your cheerios by mocking slash and the overpriced buffers he peddles.

However, my rifle, and thousands of DPMS rifles run just fine without an unnecessary "upgrade".

Regards,
 
#28
Re: DPMS 308 LR AT 1000 yards

This is the reason why I but Litz ammo and Southwest Ammo's rounds...built to the right specs and pressures depending on the bullet.

Most well built AR's should be able to shoot out to 800 easy...if they are well built and their is talent behind the trigger both a .223 and 7.62 will get to 1000 yards without problems as long as you know your ballistic charts.

I only wish I had enough room to develop custom loads but until I have enough space I will leave load development to the folks who mananufacture high end ammo and shoot it out of my high end armalite and LWRC rigs.

Might need some time working on fundamentals of trigger squeeze, bipod loading and follow through if you are experiencing that much of a difference between 800 and 1000 yards.

The Hide is right...if you have a non-clean hole at any range then your round is unstable and time to go back to the drawing board.

Happy shooting.
 
#30
Re: DPMS 308 LR AT 1000 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SteelShot11</div><div class="ubbcode-body">This is the reason why I but Litz ammo and Southwest Ammo's rounds...built to the right specs and pressures depending on the bullet.
</div></div>

Plenty of people go to long range clinics with 175FGMM or Black Hills and do fine too. Just have to choose the right bullet for the right job.
 
#31
Re: DPMS 308 LR AT 1000 yards

Thanks for all the input. Been a little busy with work but we are going to try both 155s and 178s. But I am leaning toward the 175s. SITREP in a couple weeks. I am not going to worry about the integrity of the DPMS. From what I read and experience so far, I am satisified with its operation.

Thanks everone, be back soon.
 
#32
Re: DPMS 308 LR AT 1000 yards

Went out today and tested our new load. Rig - DPMS 308LR bone stock except for the trigger (pulling the stock wanna-be military trigger was like dragging a engine block down a gravel road). Replaced it with a GEISSELE 3LBS 2stage.
Load - 178 Hornady Amax, IMR4895 42.5 grains, new Winchester brass.

First tested at 100yrds. Shot two groups of 3, (thru a chronograph 2650fps)each group the cold bore was less than .5 inch away from the two follow-up shots that literally went thru the same hole. Really, had to look close to see the hole had opened after the second shot went thru it.

Satisfied, I zeroed my scope and headed out for some 1000 yard data.

Loaded the data in a ballistic calculator and fired two shots to confirm POI elevation. Elevation was spot on, wind was varying so I had a 8inch spread.

Broke out the Kestrel, did some solid math and shot two, 3 round groups. Both sub 5 inch. Vary little variance in elevation, more wind issues.

Bottom line, I think we have the load for the DPMS. Considering the weather conditions, varieing wind with snow clouds rolling in causing consistent change in atmosphere, it was a damb good day.

Thanks for all the input.
 
#33
Re: DPMS 308 LR AT 1000 yards

great job AZElkShooter,

IMR4895 is not optimal velocity wise for 308 win for long range applications.

The Powders that will yield the highest velocities in .308 are Alliant's 2000-MR & Hogdon's CFE-223...approx 80-120+ fps over your current load.

Regards,
 
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