6.5CM AR-10 Reloading Development Help Requested

[MNtadpole]

All,
So this is the 2nd round of me trying to develop a decent load for my Daniel Defense DD5v5 20" AR-10. The 2nd round rendered a significant improvement in tighter groupings over the 1st round of development. Unfortunately, I did run into some issues that I need some advice on. Before addressing the details of this 2nd round of load development and its issues, below are the details concerning my 1st attempt during the week previously:

1st Attempt was Document Here:
https://www.snipershide.com/shootin...y-1st-6-5cm-load-development-results.7019204/

Lessons Learned from 1st Attempt:
-Increment your loads by .2-.3 grains for each string (I previously made too big of a jump)
-Don't use the Magnetospeed when testing for accuracy, but only for testing velocity
-allow the barrel to cool down significantly between strings

2nd Attempt
The goal of this session was to bring the lessons learned from the 1st attempt and grab better data for load development.
-Ladder load test by .2 grains for each increment using RE17 from 38.0 grains to 41.2grains
-Again shooting 140gr SMK bullets
-WLR primers
-Range temperature was about 74 degrees.
-Shooting 3 rounds per string at a range of 100 yards
-Used Magnetospeed to gather 1 shot velocity reading, provided that the 4th round loaded for the given charge wasn't used to compensate for a flier shot.
-Used "The Original Barrel Cooler" once the barrel became too hot to the touch. This was usually done between each string in most case, but only done as needed.

Shot Groups:
(sorry no measurements posted yet, the green target sticker is 2". I'll post update measurements tonight with fliers x'd out)

Chrono Data:

I chose to identify 39.8 and 40 grains as shooting the tightest groups

Condition of Brass from Tight Groups:

**Green arrow is pointing to some ejector pin marks noted**

**Green arrow is pointing to some ejector pin marks noted**

**Green arrow is pointing to some ejector pin marks noted**


As mentioned above, I identified the RE17 charge of 39.8-40grains giving the tightest groupings. I am having difficulty making a judgement call on the pressure indicators of the spent brass at those charges. I have identified some ejector pin rub marks. At the same time though, the WLR primers aren't appearing flatten nor are there signs of cratering around the firing pin. What should I make of these pressure signs? The Magnetospeed is clocking the velocity of these rounds at approx. 2650-2670fps, which doesn't sound like I'm really pushing it.

Issues During Range Visit:
Unfortunately, I developed a new issue during this 2nd attempt range, and oddly enough it didn't occur during my 1st attempt. I experienced 3 rounds fail to chamber correctly. The rounds appeared make it most of the way out of the magazine and wedged themselves somewhere between the barrel extension and the chamber. The BCG completely smashed these rounds, in some cases, causing the primers to pop out. Below are some of the examples of the aftermath:

After measuring my my max COL after fitting my handholds into the AR-10 P-mags, I noted that it was less than the max COL as noted in my two reloading manuals. I did decide to come back a few thousandths from the max COL as allowed from my magazine. What could be causing this issue and where should I look? I will provide the specific measurements later tonight, as they are in my reloading record book at home. I personally feel that it might be an issue related to length, but I'm not experienced enough to be certain. All my brass was full-length resized -.003 from fire-formed.

Thanks for any and all help that you can provide!

 

[Powder_Burns]

The rounds that got jacked up during chambering, I would load one in the mag and see if the bolt is locking back on the bolt catch. It could be under-gassed and the bolt is riding over the cartridge upon chambering, or the follower/mag spring are not popping up fast enough to get the cartridge in front of the bolt. If the bcg doesn’t lock back, either the loads are too light or the gun is under-gassed. If the bcg does lock back, perhaps the magazine is the culprit. Clean the magazine body, maybe replace the mag spring or try stretching it out some.

 

[BC76]

Question: are you only considering the 140g bullet? I have a RPR that loves the 147g, yet others with the same rifle use only 140/143’s. What is your barrel length? That could impact your consistency if the barrel is shorter. Also consider a different powder to see what you get out of them.
Also, what magazine are you using? You might see if you have a mag issue. Is it possible the base of the round on top is dragging the round underneath forward in the mag as it is chambered, causing the next round to jump when loaded?

 

[straightshooter1]

I don't know enough about an AR-10 to comment on what might cause that damage to the cartridges, so someone with good experience will have to chime in here. But as far as your loads go, they are as you suggest, pretty mild. . . almost too much so.

It would help to know what barrel length you're using here and what your cartridge COAL is and the ambient temperatures your shooting in. From what it looks like in your pics, the COAL's look very long. And if they are, they might be jamming into the lands causing higher pressure . . . which might produce the ejector swipe your seeing even though the powder charges are relatively light. If you haven't measured your distance to the lands to see what room you have for your jumps, it'd be a good idea to get that measurement.

Keep in mind that RE-17 is very temperature sensitive.

BTW. . . IMHO, it's not a good idea to shoot until you the barrel can't be touched (if precision is really important) as that's usually above 130°F. I will stop at 122°F to let it cool down some and I know the temperature as I have a strip (a Temperature Label) on my barrel so I can keep track of how hot the barrel it getting (especially important this time of year here in AZ).

 

[MNtadpole]

Question: are you only considering the 140g bullet? I have a RPR that loves the 147g, yet others with the same rifle use only 140/143’s. What is your barrel length? That could impact your consistency if the barrel is shorter. Also consider a different powder to see what you get out of them.
Also, what magazine are you using? You might see if you have a mag issue. Is it possible the base of the round on top is dragging the round underneath forward in the mag as it is chambered, causing the next round to jump when loaded?

I have a 20" 1:8" twist barrel. I'm not against trying other bullets, but I'm just shooting what stock I have. I'm pretty new to the reloading game. I had hoped to narrow down the best performance for this bullet/powder combination before I start introducing additional items (new powders&bullets). You know what I mean?

 

[MNtadpole]

I don't know enough about an AR-10 to comment on what might cause that damage to the cartridges, so someone with good experience will have to chime in here. But as far as your loads go, they are as you suggest, pretty mild. . . almost too much so.

It would help to know what barrel length you're using here and what your cartridge COAL is and the ambient temperatures your shooting in. From what it looks like in your pics, the COAL's look very long. And if they are, they might be jamming into the lands causing higher pressure . . . which might produce the ejector swipe your seeing even though the powder charges are relatively light. If you haven't measured your distance to the lands to see what room you have for your jumps, it'd be a good idea to get that measurement.

Keep in mind that RE-17 is very temperature sensitive.

BTW. . . IMHO, it's not a good idea to shoot until you the barrel can't be touched as that's usually above 130°F. I will stop at 122°F and I know the temperature as I have a strip (a Temperature Label) on my barrel so I can keep track of how hot the barrel it getting (especially important this time of year here in AZ).

If you're saying that the loads are too mild, what do you suggest? What are the ballpark values that I should be looking for?

Understood. I will check out getting some of those temp strips. The effects of using the barrel cooler were dramatic! I appreciate the advice.

Concerning the distance to the lands...no I have not made any measurements. I guess I figured that the COL allowed by the magazine would be smaller than what would be allowed by the rifle...that was probably not a good assumption lol. Do you recommend getting something like a Hornady length gauge with a modified cartridge?

Concerning RE-17, I was under the impression that it was supposed to be stable, relatively speaking. I understand that every manufacturer can make all the claims they want on their products and that the proof is in the pudding. With that said, here is what they advertised, of which I came to kinda understand:

The last bullet stating "consistent...velocity in extreme weather conditions" made me believe that equals non-sensitivity. I'm not trying to argue with you, I'm just trying to get smarter at this stuff. What do you make of this? If this is bad gouge, where should I go to reference an accurate depiction of powder characteristics?

 

[straightshooter1]

I have a 20" 1:8" twist barrel. I'm not against trying other bullets, but I'm just shooting what stock I have. I'm pretty new to the reloading game. I had hoped to narrow down the best performance for this bullet/powder combination before I start introducing additional items (new powders&bullets). You know what I mean?

For a 20" barrel, the MV's you're getting is very high for the powder load you're using in these cartridges. It leads me to think there is something causing higher than usual pressure to produce that kind of velocity and the ejector marks. Again . . . I'd do some measurements to see if your bullets are being jammed into the lands??? Or maybe some carbon ring issue???

 

[MNtadpole]

For a 20" barrel, the MV's you're getting is very high for the powder load you're using in these cartridges. It leads me to think there is something causing higher than usual pressure to produce that kind of velocity and the ejector marks. Again . . . I'd do some measurements to see if your bullets are being jammed into the lands??? Or maybe some carbon ring issue???

Sounds like a good place to start investigating. Guess I should look at grabbing some gauges for measuring bullet seating depth. The rifle was new before I put about 120 rounds through it, so I wouldn't imagine that there should be any blockages yet. Plus, I've cleaned the bore and barrel extension areas prior to each testing.

 

[lash]

Just a couple of observations from your target and chart:

• You DO NOT want either 39.8 or 40.0 gr load. You should not be looking for “smallest group” at this point.
• You should be looking for a stable node.
• Both your target and your chart indicate that that node is somewhere in the 40.2-40.6 range.
• Neither 39.8 nor 40.0 are in a node and are not stable.
• You chart shows both 40.2 and 40.6 at the same speed. Why did you only record velocities for every other charge?
• Your OAL does look long for a semi. If I were you, I’d find some way of verifying approximately where your lands are.

 

[straightshooter1]

If you're saying that the loads are too mild, what do you suggest? What are the ballpark values that I should be looking for?

My feeling is yes, it appears it may be too mild as 38 grs fills less than 82% of the case and 41 gr is at 88% of case. And seating them long as you're doing makes for even less percentage.

Concerning the distance to the lands...no I have not made any measurements. I guess I figured that the COL allowed by the magazine would be smaller than what would be allowed by the rifle...that was probably not a good assumption lol. Do you recommend getting something like a Hornady length gauge with a modified cartridge?

Yeah . . . you know what they say about assumptions.

The Hornady gauge works fine. Or you can use a dummy round with a loose neck configured like this:

. . . slip it in, close the bolt, extract carefully and measure. It's not likely going to be "exact", but it plenty close enough to work with.

Concerning RE-17, I was under the impression that it was supposed to be stable, relatively speaking. I understand that every manufacturer can make all the claims they want on their products and that the proof is in the pudding. With that said, here is what they advertised, of which I came to kinda understand:
View attachment 7390133
The last bullet stating "consistent...velocity in extreme weather conditions" made me believe that equals non-sensitivity. I'm not trying to argue with you, I'm just trying to get smarter at this stuff. What do you make of this? If this is bad gouge, where should I go to reference an accurate depiction of powder characteristics?

It's one of the most temperature, here's an example:

I've use this powder in my .308 cartridges and found a load that works quite well. But I decided not to use it because of this issue and the wide temperature swings I have here in AZ. Many other powders can work well with less sensitivity. But . . . these days, find the right powder available is a challenge.

BTW: Are you crimping these when building your cartridges? How much neck tension? Are you using military brass (they tend have less volume, which can increase pressure as well)? Why did you choose RE-17 for your powder of choice?

 

[BBVDD]

I did not have much luck with RL 17 in either of my guns (gasser and bolt).

RL16 was so much better and I was able to get some really hot speeds without pressure.

My gas gun’s favorite load is 140 Berger VLD hunt and 42g of H4350. No pressure there and it pushing them around 2750fps. It’s about 1/2” at 100yds with that load. Also, I was very careful to get the adjustable block dialed in just right.

 

[straightshooter1]

I did not have much luck with RL 17 in either of my guns (gasser and bolt).

RL16 was so much better and I was able to get some really hot speeds without pressure.

My gas gun’s favorite load is 140 Berger VLD hunt and 42g of H4350. No pressure there and it pushing them around 2750fps. It’s about 1/2” at 100yds with that load. Also, I was very careful to get the adjustable block dialed in just right.

Frankly, RE-17 just doesn't appear to me to be a good powder for a gas gun. Gas guns tend to be somewhat picky with regards to powder as opposed to bolt guns. RE-17 looks much too slow for a gas gun . . . as does H4350. But, as in your case, apparently an adjustable block can mitigate that issue.

 

[HemiPowrd]

Frankly, RE-17 just doesn't appear to me to be a good powder for a gas gun. Gas guns tend to be somewhat picky with regards to powder as opposed to bolt guns. RE-17 looks much too slow for a gas gun . . . as does H4350. But, as in your case, apparently an adjustable block can mitigate that issue.

I run H4350 in my 22" AR-10 6.5 CM with a heavy bolt carrier and buffer. No issues cycling at all and I run a fairly weak charge (works fine suppressed or unsuppressed). 40.3 gr, 140gr ELD-M, Lapua brass, 2660 fps. I basically just duplicated the Hornady factory 140 ELD-M ammo. One data point so take it for what it's worth.

 

[MNtadpole]

Just a couple of observations from your target and chart:

• You DO NOT want either 39.8 or 40.0 gr load. You should not be looking for “smallest group” at this point.
• You should be looking for a stable node.
• Both your target and your chart indicate that that node is somewhere in the 40.2-40.6 range.
• Neither 39.8 nor 40.0 are in a node and are not stable.
• You chart shows both 40.2 and 40.6 at the same speed. Why did you only record velocities for every other charge?
• Your OAL does look long for a semi. If I were you, I’d find some way of verifying approximately where your lands are.

I will take the node focus on board. I guess I got too caught on tightening up the groups and forgot about monitoring for nodes.

Leading up to this shooting session, I had only made 4 rounds per charge. My thought process was to do 3 round strings, while having a 4th round if I had a flier. The goal was to not have any fliers and to use the 4th round for a separate Chrono test. Because of some fliers, I did end up using the 4th round. That is why I didn't Chrono every string.

I agree that I should look into the measurement of the distance to the lands. It's an unknown at this point since I don't have a measurement. I will look into getting the supplies to measure this out soon.

 

[MNtadpole]

My feeling is yes, it appears it may be too mild as 38 grs fills less than 82% of the case and 41 gr is at 88% of case. And seating them long as you're doing makes for even less percentage.



Yeah . . . you know what they say about assumptions.

The Hornady gauge works fine. Or you can use a dummy round with a loose neck configured like this:
View attachment 7390213

. . . slip it in, close the bolt, extract carefully and measure. It's not likely going to be "exact", but it plenty close enough to work with.



It's one of the most temperature, here's an example:

View attachment 7390225

I've use this powder in my .308 cartridges and found a load that works quite well. But I decided not to use it because of this issue and the wide temperature swings I have here in AZ. Many other powders can work well with less sensitivity. But . . . these days, find the right powder available is a challenge.

BTW: Are you crimping these when building your cartridges? How much neck tension? Are you using military brass (they tend have less volume, which can increase pressure as well)? Why did you choose RE-17 for your powder of choice?

All great advice here, so thank you for that!

I will probably just put the hornady length gauges on order with some the bullet comparators too. I like grabbing tangible data. Great idea on that dummy cartridge. LOL I'll probably do it in the mean time anyways.

That's kind of a bummer on the sensitivity of the powder I chose. Yea, I bought the rifle in late May, so when it came to getting reloading material at the time, there weren't too many options due to pandemic buying . Plus, I was trying to stick to documented powders in the publications that I currently own. Do you have any suggestions of a few powders that I should keep an eye out for reloading this AR-10?

I am putting a very light crimp on the necks:

I can't answer the neck tension question yet, since I'm not quite sure how the to appropriately calculate that. I will look into getting this to you, unless you want to quickly explain the process or provide a link . The brass is Remington...nothing too nice. I do have some Hornady virgin brass waiting to be fire-formed though.

 

[MNtadpole]

Frankly, RE-17 just doesn't appear to me to be a good powder for a gas gun. Gas guns tend to be somewhat picky with regards to powder as opposed to bolt guns. RE-17 looks much too slow for a gas gun . . . as does H4350. But, as in your case, apparently an adjustable block can mitigate that issue.

What would you recommend for a gas gun? My AR-10 does have an adjustable gas block too, but I'm really not trying to mess with that variable unless I absolutely have to.

 

[MNtadpole]

I run H4350 in my 22" AR-10 6.5 CM with a heavy bolt carrier and buffer. No issues cycling at all and I run a fairly weak charge (works fine suppressed or unsuppressed). 40.3 gr, 140gr ELD-M, Lapua brass, 2660 fps. I basically just duplicated the Hornady factory 140 ELD-M ammo. One data point so take it for what it's worth.

Are you using an adjustable gas block, and if how do you have it set?

 

[straightshooter1]

That's kind of a bummer on the sensitivity of the powder I chose. Yea, I bought the rifle in late May, so when it came to getting reloading material at the time, there weren't too many options due to pandemic buying . Plus, I was trying to stick to documented powders in the publications that I currently own. Do you have any suggestions of a few powders that I should keep an eye out for reloading this AR-10?

H4895, AR-Comp, Varget

The H4895 is the fastest of the three and Varget the slowest with AR-Comp kinda in the middle. All three are faster than RE-17 as well at H4350. All three are really hard to come by in recent months. I've really come to like AR-Comp as burns rather clean and with very little copper fouling, and . . . it meters very nicely for getting consistent power measurements . . .

oh, and I've found it seems easier to produce good results on paper too.

I am putting a very light crimp on the necks:
View attachment 7390656
I can't answer the neck tension question yet, since I'm not quite sure how the to appropriately calculate that. I will look into getting this to you, unless you want to quickly explain the process or provide a link . The brass is Remington...nothing too nice. I do have some Hornady virgin brass waiting to be fire-formed though.

Neck tension is kinda a misnomer and in the reloading world it's referring to the difference between the diameter of a case before seating and the diameter after seating. With a gas gun, .003" is usually sited as minimum neck tension one should have. So, I'd say go with .003 - 004 and you shouldn't have any need for crimping.

Keep in mind that cases will have variations in neck wall thickness as much as .0015 (sometimes more for poor quality brass). You'll find such variations in Remington brass on the .0015 - .002" order (in my experience). So, if you measure the neck before seating this variation is moved to the inside of the neck and the outside has a uniform diameter due to the sizing die. Then when you seat a bullet, that variation in thickness is moved to the outside of the neck. So when you go to measure neck tension (which you may be looking for .003"), you can very well see a different measurement as you rotate the cartridge in the caliper when measuring the neck for that tension. With such irregularity in the thickness of a piece of brass, rotate to see how it measures and use an average that's close to what you're after.

 

[straightshooter1]

What would you recommend for a gas gun? My AR-10 does have an adjustable gas block too, but I'm really not trying to mess with that variable unless I absolutely have to.

With the slow powder, I have a feeling you're very likely over gassing and to get it right you really should find the accuracy load that you're going to use and then tune the gas block so that you're not over or under gassing. If you change loads (like different powder and/or bullets), you'll have to retune your gas block.

I've heard that some tournament competitors recommend shutting off the gas all together during load development, and that seems a bit tedious in having to manually extract the spent cartridge and let the bolt chamber another round. Once the cartridge development is done, then adjust the gas for it's proper function.

 

[HemiPowrd]

Are you using an adjustable gas block, and if how do you have it set?

Yes, but I just left it how it was set initially at the factory (JP Rifles). Once I added a suppressor I did adjust the gas block. The adjustment will depend on your load and gun. Basically turn the gas block adjustment way down and load one cartridge into your magazine and shoot it. If the bolt doesn't lock back increase the gas adjustment 1/2 turn. Repeat this process until the bolt locks back on the empty magazine then open the gas block 1/4 to 1/2 turn further for reliability. Load multiple cartridges into your magazine and fire them to make sure the additional cartridges feed properly.

 

[MNtadpole]

Yes, but I just left it how it was set initially at the factory (JP Rifles). Once I added a suppressor I did adjust the gas block. The adjustment will depend on your load and gun. Basically turn the gas block adjustment way down and load one cartridge into your magazine and shoot it. If the bolt doesn't lock back increase the gas adjustment 1/2 turn. Repeat this process until the bolt locks back on the empty magazine then open the gas block 1/4 to 1/2 turn further for reliability. Load multiple cartridges into your magazine and fire them to make sure the additional cartridges feed properly.

Okay that makes sense. In the lovely state of IL, the government has decided that suppressors are too much fun for the citizens and therefore banned them. SMH. It sounded like someone was suggesting to compensate for the short comings of a particular powder by adjusting the gas block. Maybe I misunderstood, but I'm not really trying to mess with it. Well, at least not in this stage of the game for me...I still have much to learn.

 

[HemiPowrd]

Okay that makes sense. In the lovely state of IL, the government has decided that suppressors are too much fun for the citizens and therefore banned them. SMH. It sounded like someone was suggesting to compensate for the short comings of a particular powder by adjusting the gas block. Maybe I misunderstood, but I'm not really trying to mess with it. Well, at least not in this stage of the game for me...I still have much to learn.

It wouldn't be a bad idea to adjust your gas block once you settle on a load. You might be somewhat over gassed at that point so it couldn't hurt just to verify it is properly adjusted.

 

[greg1147]

Lot of good tech here I haven't had any issues with AR10 6.5CM except getting the gas block set. I run a suppressor most of the and get good ejection pattern and no feeding problems. With the suppressor removed it sends brass at 0100-0200 oclock figure the removal of the suppressor creates an over gassing issue.