Ins and outs of OCW with a semi auto.

[Halfnutz]

When working through an OCW test in a semi auto, namely an AR platform, do you single load by releasing the bolt catch or load them from a magazine? Max load first in the mag and decrease incrementally each successive round.
I'm thinking Single load is the way to go? Any opinions?
Working on 6.5CM 140gr MK with 4831sc. Next will be Win StaBall 6.5.
22in AR, 1in10 twist.

 

[Doom]

Either way should work. The thing you need to be concerned about is bullet setback with the mag loads. With the MK I would recommend a Lee FCD to minimize the possibility.

 

[spife7980]

I put my round in the top of the mag, insert it and usually the bolt is locked back so Ill hit the catch and let it fly.

I also always keep one extra round in the mag, I find that the last round out of a mag has a high probability of being different than all the others when the bolt locks back.

Since I keep that extra round, it gets chambered after my intended shot. When I eject it the bolt locks back, thats why I start fro a locked back bolt as I mentioned at the start.

 

[Halfnutz]

I put my round in the top of the mag, insert it and usually the bolt is locked back so Ill hit the catch and let it fly.

I also always keep one extra round in the mag, I find that the last round out of a mag has a high probability of being different than all the others when the bolt locks back.

Since I keep that extra round, it gets chambered after my intended shot. When I eject it the bolt locks back, thats why I start fro a locked back bolt as I mentioned at the start.

Makes sense. I didn't consider adding another round. Thanks!

 

[W54/XM-388]

Some pistol systems cause a bit too much stress on the extractor if you manually stick a round in the chamber and let the slide go.
You might want to check, but some types are better loaded from the magazine.

 

[Srikaleak]

Instead of

I also always keep one extra round in the mag, I find that the last round out of a mag has a high probability of being different than all the others when the bolt locks back.

Since I keep that extra round, it gets chambered after my intended shot. When I eject it the bolt locks back, thats why I start fro a locked back bolt as I mentioned at the start.

Could you utilize a snap cap instead of a live round to reduce that locking back variability? I would think a bullet being chambered twice would affect it somewhat.

 

[2aBaC̶a̶]

Some pistol systems cause a bit too much stress on the extractor if you manually stick a round in the chamber and let the slide go.
You might want to check, but some types are better loaded from the magazine.

Interesting, i wonder why it would matter? Either way the extractor doesnt engage until the bolt slams into the back of the case in the chamber.

I've loaded for but yet to do an OCW on a semi but I would think a single feed closing the BCG as gently as possible would prevent any influence from the action on the loaded round.

My 6.5CM AR marks up bullets pretty bad when feeding from a mag. I need to fix that.

 

[spife7980]

Instead of

Could you utilize a snap cap instead of a live round to reduce that locking back variability? I would think a bullet being chambered twice would affect it somewhat.

I don’t care what that single round that I repeatedly use for each test does, it’s not part of the test.
And how is not locking back on a snap cap any different than not locking back on any other round since the magazine still isn’t catching it? What’s happening before is still happening before just the same.

 

[Halfnutz]

Granted I'm still learning to drive this thing. A large frame AR is definitely different than a bolt rifle.

I loaded a factory round in the mag first then the test round. Fired the test round and repeated. The factory round was kinda beat up from the repeated chambering by the time I got through 4 rounds of 7 charge weights plus a single max load round. I'm happy with this process.

What I learned.
1. I need to practice alot more with this platform. Obviously.

2. The extra round in the mag gave the same recoil pulse after the shot, but it would have been the same without it albeit the bolt locking back does feel different on the follow through.

3. My Max charge weight was published at 45.6gr of H4831sc, I did not have any pressure signs, at all. Should have loaded more rounds than just one, and possibly another round .3 over.

4. 4th group is probably my OCW. But the third group could've been me. SD was 4 on group 3.

5. Hornady 140gr eld Match runs average of 2665 fps with an SD of 14. My OCW is 100+ fps slower. H4831sc is probably not the powder I want if I wanna run at 2650+.

6. My cold bore is a bitch.

 

[Halfnutz]

Oh and
7. It was a beautiful day to be at the range.

 

[supercorndogs]

Interesting, i wonder why it would matter? Either way the extractor doesnt engage until the bolt slams into the back of the case in the chamber.

I've loaded for but yet to do an OCW on a semi but I would think a single feed closing the BCG as gently as possible would prevent any influence from the action on the loaded round.

My 6.5CM AR marks up bullets pretty bad when feeding from a mag. I need to fix that.

Controlled feed is what makes the difference. Some guns are made so that the extractor is engaged with the extractor grove while the round is being fed into the chamber. Some of these don't have room for the extractor to pop over the rim. A 1911 for example, if you do that it can bend the extractor, I did it to mine. I had to pull the extractor and re tune it. I.E. bend it back. LOL

If we are getting that far out in the weeds. Would you not want to fire a round and have your test round fed into the chamber as a gun would normally function? As well as having another round below so it doesn't lock open? ?

Last one I did I just loaded up the mag in order. 23.something of 8208 is the easy button, but I am out of 8208 and can't find more. ?

 

[Halfnutz]

Ideally, I would want them all to feed as normal, but with 28 test rounds plus one "max", not all would fit in the mag and I was trying to keep the barrel cool.
Also wanted to keep track of them. I know me, and sitting there thinking was that the 4th or 5th charge weight was likely, especially after a rare but possible 2 in 1 hole. In addition, I was switching the chrono through strings and didn't want to be in front of a loaded rifle.
With less charge weights and leaving the chronograph out of it, I would agree otherwise with 1st round sighter, 1,2,3,4,5, 1,2,3,4,5, 1,2,3,4,5, 1 at max and last round over max load to lock the bolt open. 18 total.
Now I need to decide next time if 3 rds is sufficient or should I do 5? I did 4 this time of each just in case I knew I had a driver induced flier. I did 7 charge weights because I am new to loading 6.5CM, there is also not a lot of data for H4831sc. I had the powder on hand and wanted to get a feel for it all.
I learned a bit, burnt up a some powder that was sitting around, as well as got some practice in. Right, wrong, or Indefferent, I'll chalk it up to experience.

 

[Dobbs02si]

Maybe I'm missing something, but what affect does the bolt locking open or going back home have on a bullet that is already at a 100yd target before the bolt locks back up? I understand the follow through after the trigger breaks, and two completely different sensations on last round lock vs going back home, I just can't grasp what affect it has on the pill that's not in the barrel when either scenario is taking place.

I'm a bolt guy so just trying to understand why what is what with the lego guns.

 

[Halfnutz]

Easing the bolt forward or hitting the bolt release both potentially effect the round seating in the chamber differently. No forward assist on my AR10 either, even then the potential exists. For the OCW I hit the bolt release. You are probably correct on the bullet being uneffcted by the bolt locking open. BS or not I felt better about my follow through.

Maybe I'm missing something, but what affect does the bolt locking open or going back home have on a bullet that is already at a 100yd target before the bolt locks back up? I understand the follow through after the trigger breaks, and two completely different sensations on last round lock vs going back home, I just can't grasp what affect it has on the pill that's not in the barrel when either scenario is taking place.

I'm a bolt guy so just trying to understand why what is what with the lego guns.

 

[2aBaC̶a̶]

Controlled feed is what makes the difference. Some guns are made so that the extractor is engaged with the extractor grove while the round is being fed into the chamber. Some of these don't have room for the extractor to pop over the rim. A 1911 for example, if you do that it can bend the extractor, I did it to mine. I had to pull the extractor and re tune it. I.E. bend it back. LOL

If we are getting that far out in the weeds. Would you not want to fire a round and have your test round fed into the chamber as a gun would normally function? As well as having another round below so it doesn't lock open? ?

Last one I did I just loaded up the mag in order. 23.something of 8208 is the easy button, but I am out of 8208 and can't find more. ?

Right but aren't we talking about an AR platform? Last I checked theres no control round feed.

And yes you should test from mag as you would use it but knowing the optimum accuracy without mechanical influence can be beneficial. Most of the things we do is to limit or eliminate factors of influence. The way I see it If you know it shoots 1/2" single fed, but only does 1" mag fed then you can try to figure out why mag fed is causing it. If you chose to mag feed you wouldnt know it's full potential.

A bullet being fed from a mag has more of a chance of having something happen to it before it even reaches the chamber that will effect down range performance.

Which is probably more of an overall functionality thing rather than part of an OCW accuracy test.

 

[2aBaC̶a̶]

Maybe I'm missing something, but what affect does the bolt locking open or going back home have on a bullet that is already at a 100yd target before the bolt locks back up? I understand the follow through after the trigger breaks, and two completely different sensations on last round lock vs going back home, I just can't grasp what affect it has on the pill that's not in the barrel when either scenario is taking place.

I'm a bolt guy so just trying to understand why what is what with the lego guns.

I'm more of a semi auto guy and wondering the same.

 

[spife7980]

I don’t think it’s the bolt catching on the mag but not having that round pressing up against it dragging the bolt changing it’s harmonics and unlocking and timing.
Idk, but it only took me one round of testing with every single last round flying way outside the group to surmise that it had an effect. And its not just me noticing, it’s been discussed before, easy to test it for yourself.

 

[supercorndogs]

Last and first round fliers are pretty well documented in AR-15s.

 

[FCS]

First rd out of magazine is chambered with a different BCG speed / momentum. Many times this causes round to be out of core group.
Last round out of magazine, no ammo pushing up on bottom of bolt carrier so there is slightly different support on case head. Many times this causes round to be out of core group.
Both are well documented.

I test AR loads as they will be used; how load behaves as a single shot isn’t the same as how ammo behaves when used as a gas operated system. Experienced this a time or two, seen this happen to others many more times.
Test the whole system (rifle, ammo, magazines, optic, bipod & rear bag or slung up) in the way you’ll be using system. IMHO, you’ll be farther ahead, have the system better optimized testing how system will be used majority of the time than if test ammo one way but actual use is significantly different.

140 SMK, 6.5 Creed gas gun you’ll be a little slow with 4831sc for velocity, port pressure will be a little higher even though peak pressure is lower.
How long is gas system?
How heavy is buffer?
10 twist barrel? If really a 10 twist, I’d be looking at lighter bullets as 140s, even the 140 SMK w/8-10 ogive radius, probably won’t be stabilized with a 10 twist bbl.
140s do well with H4340, possibly H414/Win 760 (too temp sensitive for my liking), possibly IMR4451, maybe IMR4955. AA4350 is usually a smidgen faster in burn rate than H4350, might work well in gas gun application w/140 SMK.
I haven’t tried StaBall 6.5 yet, not a fan of ball powders if I can avoid them.

130 AR Hybrid is the Goldie Locks bullet for BC / velocity for 6.5 Creed gas gun, in my testing / experience. 130 TMK / ELD-M probably in mix also, I’ve not had a reason to stray from the Berger.

 

[flyright]

I've found that holding the rifle with the same pressure as when firing, while dropping the bolt for the first round, helps keep that first round in the group. Also, as the rifle breaks in, the first round flyer usually gets much better or goes away. I agree with FCS on the last round flyer. My rifles don't seem to have that problem but I've seen it several times on some cheap/home builds. I've always attributed it to an inferior bolt lock up but I could be wrong.

 

[Halfnutz]

First rd out of magazine is chambered with a different BCG speed / momentum. Many times this causes round to be out of core group.
Last round out of magazine, no ammo pushing up on bottom of bolt carrier so there is slightly different support on case head. Many times this causes round to be out of core group.
Both are well documented.

I test AR loads as they will be used; how load behaves as a single shot isn’t the same as how ammo behaves when used as a gas operated system. Experienced this a time or two, seen this happen to others many more times.
Test the whole system (rifle, ammo, magazines, optic, bipod & rear bag or slung up) in the way you’ll be using system. IMHO, you’ll be farther ahead, have the system better optimized testing how system will be used majority of the time than if test ammo one way but actual use is significantly different.

140 SMK, 6.5 Creed gas gun you’ll be a little slow with 4831sc for velocity, port pressure will be a little higher even though peak pressure is lower.
How long is gas system?
How heavy is buffer?
10 twist barrel? If really a 10 twist, I’d be looking at lighter bullets as 140s, even the 140 SMK w/8-10 ogive radius, probably won’t be stabilized with a 10 twist bbl.
140s do well with H4340, possibly H414/Win 760 (too temp sensitive for my liking), possibly IMR4451, maybe IMR4955. AA4350 is usually a smidgen faster in burn rate than H4350, might work well in gas gun application w/140 SMK.
I haven’t tried StaBall 6.5 yet, not a fan of ball powders if I can avoid them.

130 AR Hybrid is the Goldie Locks bullet for BC / velocity for 6.5 Creed gas gun, in my testing / experience. 130 TMK / ELD-M probably in mix also, I’ve not had a reason to stray from the Berger.

Gas system is rifle length.
Running an H2 buffer.
The rifle is a LaRue Ultimate Upper kit /w Burris XTR 2 5-25x50. Magpul PRS stock.

I've tried some FGMM w/130gr Berger OTM. They did shoot well.
Thanks for all the input, much appreciated.

 

[Halfnutz]

The 140's are Midway factory 2nds. I made the assumption they are Sierra MK. The 130's I have are also 2nds.

 

[FCS]

Gas system is rifle length.
Running an H2 buffer.
The rifle is a LaRue Ultimate Upper kit /w Burris XTR 2 5-25x50. Magpul PRS stock.

I've tried some FGMM w/130gr Berger OTM. They did shoot well.
Thanks for all the input, much appreciated.

I'm pretty sure the UUK 22" has a longer than rifle length gas system, should be an 8 twist barrel.
Running LaRue supplied gas block or an adjustable?
I'd heavy up buffer to at least an H3, heavier would be more better.
Using a Magpul PRS stock, I'd change parts around so that you can use a rifle buffer tube & -10 rifle buffer. Heavy up buffer to help keep bolt locked up longer if you want to run the heavier match bullets. Take advantage of the ability to run a rifle buffer and heavy it up using tungsten weights if using the PRS stock vs a CAR buffer tube buttstock.

 

[Halfnutz]

Larue provided gas block.

Per Larue:
1 in 10
Rifle length +2
The PRS is on a Larue provided rifle buffer tube that has spacer so the interior is carbine length. I had to order this separate from the UU kit.
I've read because of the lack of standardization on Ar10's that the buffer tubes can be hit or miss for fit, IIRC the thread length may interfere with buffer retention pin. I will consider an H3 buffer. I run a Super 42 Geissele spring and H2 in my 18" LMT MRP and it seems to help on the AR15 size.

Thanks again for the input.