That Love / Hate thing again, GAP 10 with 4895 and 175 SMK's

[308sako]

I started with a clean oil only lubed rifle and the Winchester brass with IMR 4064, a load that has shot well... it still does with 100% function. Next I went a little higher than previously with 4064 to gather data and wear this rifle out. The rifle functioned 100% to the 42.3 grain load velocity 2546, SD 14. 42.5 did not feed nor lock back on empty.

41.5 grains 4064, Winchester brass Federal 210 primer 175 SMK @ 2.785" Vel = 2501 SD 14
42.1 grains 4064, Winchester brass Federal 210 primer 175 SMK @ 2.785" Vel = 2535 SD 26
42.3 grains 4064, Winchester brass Federal 210 primer 175 SMK @ 2.785" Vel = 2546 SD 14
42.5 grains 4064, Winchester brass Federal 210 primer 175 SMK @ 2.785" Vel = 2570 SD 7

Now with a fouled barrel I switched to IMR 4895 and the LC LR cases and low starting load of 39.0 grs function was 100 % feeding thru the 40.2 grain charge. However there was no lock back on empty ever with this powder (WTF) Worse part about that is it was the most accurate powder yet. Targets are 4895 top 2, 4064 bottom. The loads were all shot top left and clockwise around that paper. So 39 - 40.2 on upper left, and 40.6 - 41.8 upper right. 4064 41.5, 42.1, 42.3 and 42.5 on bottom. I should add that the bolt catch barely does so even when doing so manually, and when inserting a magazine it is more than likely to let go...

39.0 grains IMR 4895 LC 11 LR cases Federal 210 primers 175 SMK @ 2.785" Vel = 2361 SD 9
39.4 grs Vel = 2408 SD 8
39.8 grs Vel = 2439 SD 16
40.2 grs Vel = 2465 SD 10
40.6 grs Vel = 2483 SD 6
41.0 grs Vel = 2517 SD 5
41.4 grs Vel = 2544 SD 13
41.8 grs Vel = 2582 SD 12

IMR 4064 appears to be the winner for function and accuracy repeatable at this point. I am losing faith that the rifle will function with the suppressor once that happens. It is a very narrow window of acceptable pressure apparently to guarantee function. What I had learned since the prior post is that the rifling will engage the bullet with a cartridge length of 2.810" average. So I have now changed my cartridge length to 2.785" and Pmags like that better too. Total known rounds fired: 206.

 

[jaycoux]

I would call GAPrecision. I believe you should be loading to 2.80 and that should not be a problem. You should not have to load to 2.785. Changing seating depth that much on a previously successful load can change things significantly. Dont forget to SB resize even new brass as well.

 

[Notso]

Disappointing that a rifle this expensive and well regarded is so finicky.

 

[tipper]

42.5-43.5 of 4064 is the load George said, I think there for you should ask him. If you are going to run a can should it not be on for testing loads.

 

[cruze5]

which GAP 10 do you have? the armalite build or the newer?
i haven't had these functionality issues with mine but i can't seem to get it to calm down for accuracy.
had a HS match trigger installed, but haven't had the chance to go to the range

after reading your last thread i took George's advice and i have switched to triflow for my ar's.... hopefully that will work the same.

edit... pmags... disregard my question

 

[jaycoux]

42.5-43.5 of 4064 is the load George said, I think there for you should ask him. If you are going to run a can should it not be on for testing loads.

That is not the load or even the powder that george recommended as i recall. He recommended 42.5 of varget for 175 SMK and 43.5 for 168 SMK. Also complicating this is 2 different cases that have very different capacities, so its not an apples to apples comparison. I dont know what cases george was referring to when he made that recommendation. I would assume LC cases since that is what the op had at the time, but you will have to ask him that.

 

[ZLBubba]

Yup, there's way too many variables in these equations. Choose whatever bullet you want to use (mine likes the 175SMKs the best), then stick with the same virgin brass (I use Lapua), primers, and powder (I use exclusively Varget) throughout the load up process. Keep the seating depth just below mag length. See how it shoots.

Is the primary concern accuracy, reliability, or both? Because if those are your core issues, then I'd get some of the SW, McCourt, or Copper Creek gas gun 308 loads and shoot them so that you have a baseline of accuracy and function. Right now I don't think any of us can tell whether the issue is the gun or the reloads, and that's a problem. That's not a ding on you, just too many variables throughout this process have muddled the outcomes somewhat.

The good news is that the second you get fed up with that rig, you can put it up for sale and it will be gone within the day. Silver linings, man...

 

[jaycoux]

Agreed. There is NO reason why that rifle shouldnt shoot bugholes AND function flawlessly if you use small base resized LC brass, 42.5 ish varget and 175 SMKs seated to 2.80. If you have problems with that it needs to go back. Its as simple as that....

 

[308sako]

Yup, there's way too many variables in these equations.

I totally agree with that comment, and fully intend to diminish the variables.


Choose whatever bullet you want to use (mine likes the 175SMKs the best), then stick with the same virgin brass (I use Lapua), primers, and powder (I use exclusively Varget) throughout the load up process. Keep the seating depth just below mag length. See how it shoots.

Is the primary concern accuracy, reliability, or both?

We all know that "only accurate rifles are interesting" but functionally reliable is essential in this case.

Because if those are your core issues, then I'd get some of the SW, McCourt, or Copper Creek gas gun 308 loads and shoot them so that you have a baseline of accuracy and function.

Right now I don't think any of us can tell whether the issue is the gun or the reloads, and that's a problem. That's not a ding on you, just too many variables throughout this process have muddled the outcomes somewhat.

You are absolutely correct.

The good news is that the second you get fed up with that rig, you can put it up for sale and it will be gone within the day. Silver linings, man...

No so quick! The rifle is only 2 weeks old, it took over a year from the order date to receive this rifle, give it a chance, I sure am.

Next stop will be back to Varget and the 175's... probably in new commercial brass (finally.)

 

[InkedIan]

Next stop will be back to Varget and the 175's... probably in new commercial brass (finally.)

If you can't find varget you might want to try PP 2000mr. With 46.8grs of 2000mr i'm getting about 2570fps with 178gr HPBTs with great accuracy, about 4-5fps SD's, and no pressure signs from my 18.5" gas gun.

 

[Notso]

I know this is more of a reloading forum question, but it applies to the GAP issues stated by the OP..... but what do small base dies do that regular FL dies do not and what about the GAP configuration requires SB dies? Sorry, that was actually two questions.

I'm not saying the advice to go to SB dies isn't completely valid - I'm just trying to understand the logic and the physics as to why that will change the outcome.

 

[c4xplsv]

Regarding small base dies...

http://www.midsouthshooterssupply.com/ar_dies.asp


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[sib1948]

Sounds like the solution to many AR reloading issues.

 

[Notso]

Regarding small base dies...

RCBS® AR Series Die Sets | Midsouthshooterssupply.com

Thanks, that helps. But this part doesn't make sense (from your link):

2. What is a Small Base Sizing Die or maybe a better question would be why would I need it?

A Small Base sizing die is a little tighter in the web area than a Full Length Sizer. Semi Auto, pump and lever action rifles tend to have tighter chambers than bolt action rifles, thus requiring the tighter small base sizer.

I thought just the opposite was true that semis generally have looser chambers than bolt guns because of the need for rapid feed and extraction.

 

[c4xplsv]

That part of the link seems a little backwards to me as well.

This is from my own observations however...

1. Semi autos extract the brass immediately (duh right?) unlike bolt guns. Therefore the brass is more "out of shape" because it didn't have those extra seconds to cool in the chamber like a bolt gun.

2. Try to put a piece of once fired semi auto brass back into the chamber of any gun (good luck!) - it's going to stick.

3. My biggest problems with sizing rifle brass came from trying to use a progressive press to do the resizing - mine was a Hornady Lock 'n Load progressive. The small base die helped a little but ultimately I didn't solve the "sticking" problem until I just got a single stage press (RCBS rock chucker) for all my rifle cartridge resizing. Problem solved - never looked back (6 yrs ago).

4. The article references "cam over' - you don't need much but I found that typically you DON'T need a small base die if you do this (normal die works just fine for me). Progressive presses don't do the 'cam over' thing very well - hence my remarks in 3.

5. I have found that sometimes I have to resize semi auto brass more than once (2-3 times into the die) to get it to size down for a bolt gun using regular dies.

What's the bottom line here?

Small base dies are designed to be more aggressive and therefore increase reliability of feeding. Does everyone need them? No. Are the needed for certain rifles? I suppose so - but I would take it on a case by case basis.


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[InkedIan]

I feel lucky.... I only neck size my fired brass for my gas gun with zero problems.


.

 

[308sako]

I feel lucky.... I only neck size my fired brass for my gas gun with zero problems.


.

Just whose gas gun do you have?

 

[InkedIan]

Just whose gas gun do you have?

I put it together...

It's a R25 with:
FA 18.5" barrel, Rifle length GS, They use what they call a "hybrid chamber" Which I think it's called that because of the throat and not the chamber dimensions. Kinda of like the 223 wylde chamber, but I'm assuming.
JP adjustable Gas block
FA bolt
and other stuff that doesn't affect that.

After the the brass is once fired I only neck size until the brass primer pocket is too loose(federal brass is soft) or it's too damaged.

 

[tipper]

Hard Swallow, must be a lite load.

 

[lte82]

Its not your load or your shooting / driving or whatever. I would verify the gas block gas port is centered perfectly over the barrels gas port, verify that the gas tube is centered with the bolt carrier gas key and not dragging, ensure there is zero binding between the bcg and trigger hammer (no hammer wedging), the gas block is properly tightened down (when it heats up, if its not clamped on tight gas can start escaping), and make sure the barrels gas port is the correct dimension and not undersized slightly. If thats all good, have someone bore scope the chamber and make sure everything is smooth and there arent any tooling marks that could cause the chamber to "grip" the brass.

For the hell of it, try a small base die as well. I know some chambers really benefit from it, while others dont.

Last, what is the inside diameter of your fired brass? Could the chamber be cut so short and / or tight that the neck is getting stuck? If you are seeing pressure signs prematurely then that could be a rabbit worth chasing.

 

[308sako]

Its not your load or your shooting / driving or whatever. I would verify the gas block gas port is centered perfectly over the barrels gas port, verify that the gas tube is centered with the bolt carrier gas key and not dragging, ensure there is zero binding between the bcg and trigger hammer (no hammer wedging), the gas block is properly tightened down (when it heats up, if its not clamped on tight gas can start escaping), and make sure the barrels gas port is the correct dimension and not undersized slightly. If thats all good, have someone bore scope the chamber and make sure everything is smooth and there arent any tooling marks that could cause the chamber to "grip" the brass.

For the hell of it, try a small base die as well. I know some chambers really benefit from it, while others dont.

Last, what is the inside diameter of your fired brass? Could the chamber be cut so short and / or tight that the neck is getting stuck? If you are seeing pressure signs prematurely then that could be a rabbit worth chasing.

Based on the original LR 118 cases, loaded necks were .3393", fired they are .3460" at the shoulder junction and .3430" near the mouth of the case. Body of the case just behind the shoulder is .449 expands to .454 after firing, mid body is .458" before and .4615" after firing. The case just above the extraction groove (solid head portion) is .4684" and .4693" after firing. Cases have always been trimmed to 2.008" before seating a bullet.

Virgin brass of which I have several types in house have smaller dimensions than the above example/experiences.

Thanks for your thoughtful comments.

 

[lte82]

Based on the original LR 118 cases, loaded necks were .3393", fired they are .3460" at the shoulder junction and .3430" near the mouth of the case. Body of the case just behind the shoulder is .449 expands to .454 after firing, mid body is .458" before and .4615" after firing. The case just above the extraction groove (solid head portion) is .4684" and .4693" after firing. Cases have always been trimmed to 2.008" before seating a bullet.

Virgin brass of which I have several types in house have smaller dimensions than the above example/experiences.

Thanks for your thoughtful comments.

It sounds like your brass has plenty of clearance, with the neck being somewhere close to SAAMI minimum. I don't think a SB die would do any good.

Good luck with this... I hope you are able to get this solved.

 

[308sako]

This should be the last post hopefully as I feel the rifle is doing it's part now.

http://www.snipershide.com/shooting...eorge-will-you-forgive-me-gap-10-breakin.html

I will explore the upper boundaries with the Winchester brass and look again to 4895 as that powder has accuracy in this tube written all over it.

 

[Notso]

This should be the last post hopefully as I feel the rifle is doing it's part now.

http://www.snipershide.com/shooting...eorge-will-you-forgive-me-gap-10-breakin.html

I will explore the upper boundaries with the Winchester brass and look again to 4895 as that powder has accuracy in this tube written all over it.

Holy crap SAKO, that's some good shooting! Nice to see the brass change seemed to help.