308 Factory vs Hand Load Question

[DMW1116]

I'm loading 175 grain SMK bullets to replicate Federals Gold Medal Match. I'm shooting them out of a semiauto with an adjustable gas block. If the hand loads will lock back the bolt, but the factory loads won't on the same setting, does that mean the hand loads are faster, or just make more gas to cycle the action better?

ETA: no I don't have a chronograph.

 

[Bfh_auto]

It could be either. Are you using the same powder as the factory ammo?

 

[MEHavey]

I'm loading 175 grain SMK bullets to replicate Federals Gold Medal Match.

By "replicate," do they chronograph the same ?

 

[Blue68f100]

Different powder = different gas pressure curve.

Do they shoot the same POA=POI?

This is where a crony is nice for comparison.

 

[Reloadron]

This is where one needs to really look at the pressure curve and also the velocity. Less a chronograph you really don't know what you have. What are you loading as in the load data including primer?

The following is arguable and just something I read and took note of.
Sierra 168 MK
43.5 IMR 4064
Fed 210m primer

For the 175 MK
41.8 grains of IMR 4064

Now how those stack up I really don't know. While I still have a few boxes of the Federal 168 grain MK bullets I load mostly AA2495 for my AR 10. While the above loads look reasonable I really can't swear they duplicate Federal's load and Federal's choice of cannister powder.

Do they shoot the same POA=POI?

That would be all I was concerned with.

Ron

 

[DMW1116]

No chronograph data yet. My hand loads are more accurate but I'm guessing on velocity. I was hoping the difference in locking back the bolt meant higher velocity but I sorta figured there were too many other reasons for the difference.

 

[DMW1116]

They shoot very similar in terms of POI/POA.

My most accurate load is 42.5 grains of IMR 4064, CCI #34 primers, 175 gr SMK, 2.800 to 2.805 COAL. It just locks the bolt back. One more click closed on the gas block and it will eject, but won't lock back on the last round.

 

[FROGO207]

Someone might run your specs through quickload for you. Also someone might have real world Federal GMM velocity but it still is an unknown without the factory propellant data. As long as the rounds you make operate the rifle and are accurate I would not worry about it.

ETA A fair number of my firearms have never had a factory round through them as I prefer my more accurate handloads for them. YMMV

 

[bigpower491]

Just so happens I was working with some similar loads to yours, with 168 SMK and 4064 this afternoon.
20" barrel and 41.2gr was running right at 2400 out of the DPMS LR. Thats about as high as I like to throttle that rifle, and she was doing around an inch at 100.

 

[DMW1116]

I hear you on backing off full throttle. My most accurate loads generally have been in the middle range of the load data. I'm working on a 180 grain hunting load for this rifle, and in that case I would probably be willing to sacrifice some accuracy for velocity. For the 175 gr SMK load I don't want to do that. I'll just have to buy or borrow some chronograph time.

 

[Archie]

Regardless of velocity, the factory loads NOT locking the bolt indicates the load (whatever it is) generates LESS gas pressure at that late point when the bullet passes the gas port. So, reasonably, the hand loads keep the pressure level up longer indicating a slower powder.

I know in Garands and M14 rifles (I presume the M1A replica) the condition of a high gas port level can bend operating rods and peening some parts - over time - and just cause wear and tear more quickly. The muzzle velocity - when you have or can use a chronograph - is NOT a reliable predictor of internal pressure.

I do not know what model rifle you are using. That bit of information might or might not provide a clue.
I would suggest you, after consulting reloading manual, switch to a faster powder and therefore use less of a charge. Barring that, have a chat with someone who has the same rife as you and compare notes.

 

[DMW1116]

I'm using an AR10 platform. I will have to check my manual but I just bought some CFE 223. It might be faster. It is another powder that is usable in all the rifle rounds I reload, but actually gives a higher velocity in this load than my usual IMR 4064.

 

[MEHavey]

QuickLoad says it should easily function as designed.
55ksi Chamber/12ksi at 15" port

 

[DMW1116]

I'm not familiar with Quickload. Is that load development software?

At least that's reassuring. The 42.5 grain load has been more accurate than I'd ever expected out of this rifle. Load data goes all the way to 45 grains, but I never tried that. I saw some cratering and flattened primers in the 43 to 44 grain range.

 

[cfullgraf]

I'm using an AR10 platform. I will have to check my manual but I just bought some CFE 223. It might be faster. It is another powder that is usable in all the rifle rounds I reload, but actually gives a higher velocity in this load than my usual IMR 4064.

FYI, in the Garand, slower burning powders create a higher port pressure that is detrimental to the life of the op rod system. Newer powders that have been developed since WWII that are suitable for a 30-06 rifle burn slower than what is acceptable for the Garand. That is the reason that a couple gas pressure reduction plugs on the market developed for the Garand are available.

The AR-10 has a completely different gas system than the Garand. I'm not familiar with the port pressure limitations on AR-10 are, but I am sure the the AR-10 has different requirements from the Garand.

I use CFE223 in my AR-15 204 Ruger loads in a 26" AR-15 prairie dog rifle and it performs well. For reliable functioning of the AR-15, I had to increase the weight of the buffer to slow the bolt down. An adjustable gas block would do the same but the rifle was built and the heavier buffer was the easier solution.

 

[kelbro]

I'm not an AR-10 guy...is the bolt supposed to lock back?

If the factory loads do not lock the bolt back and your reloads do, I would be questioning the pressure of the reloads.

If you had primer indicators at 43 and you are shooting at 42.5, you might be pushing it. Do the factory load primers look good?

Chrono would be good now to really understand the load differences.

 

[DMW1116]

The AR10 is the predecessor to the AR15 and basically works the same. The bolt should lock back on the last round. This one has an adjustable gas block that is click adjustable. It was set from the factory at full open (18 clicks) so it would basically cycle anything.

My hand loads will cycle with the gas block closed 6 clicks, but won't lock the bolt back unless it's at 5 clicks closed. The Federal GMM needs 4 clicked closed to lock the bolt back. I originally set the gas block with Federal 150 gr soft point. This locked the bolt at 7 clicks closed, but wouldn't reliably eject at 8.

I say all this to make sure I'm not thinking about it backwards. The Federal GMM has less pressure overall, therefore needs the gas block open a bit more to get full function. The 150 gr soft points generate higher pressure overall and only need the gas available after closing the block down 7 clicks from fully open. My hand loads are in between, requiring 5 clicks closed. Does that make sense to anyone but me?

 

[bigpower491]

So set the block where all of it functions reliably and leave it.

 

[243winxb]

Port pressure & burn rate of the powders used are different. Adjust gas block.

 

[MEHavey]

If I read what you wrote correctly . . .
Federal/Commercial needs more (1-click more) gas port opening to lock back, than your 4064-based reloads.

2 thoughts:
- Leave things at Federal/4 clicks closed position.
- Walk away...

 

[bigpower491]

I'm not familiar with Quickload. Is that load development software?

At least that's reassuring. The 42.5 grain load has been more accurate than I'd ever expected out of this rifle. Load data goes all the way to 45 grains, but I never tried that. I saw some cratering and flattened primers in the 43 to 44

Ok.....ill tell you right now that quite hot for an AR10. I always use service rifle data for that DPMS, and none of the data i have go past 42gr with IMR 4064 with my 168 SMK or 168 A Max, the 2 projectiles of put thru it.

 

[Blue68f100]

I shoot an AR 10 in 6.5 CM. I have a Silent Capture Buffer spring setup in mine. I use MAX Buffer Weight, all tungsten. I also have a adj gas block. What you want is the brass to exit in the 3:00 - 4:30 direction. You should be able to do that with the adj gas block, set it and be done. Depending on who's bolt your using I've seen many where the FP hole is over size causing primer flow. Some mistake this as primer flow around the edges, it's not the same. The best fix is to replace the bolt with a correctly fitted pin/hole tolerance. JP Enterprise sells the best HP bolt that I have found. I've repaired several by installing a bushing to tighten up the tolerance on some.

 

[DMW1116]

Ok, so I guess the next step is to try some more factory ammo and see how that works.

Ejection is right in that range. Some is at 3 and the stuff I tried yesterday was about 4. Yesterday was a 180 gr hunting load with 41.7 gr of IMR 4064. I need to clean it today, so I'll check everything out while its apart. I took it apart last weekend and cleaned it after shooting a few loads for testing. I didn't see any issues inside, but it has less than 100 rounds through it.

 

[bigpower491]

Maybe try some Varget if you happen to have some

 

[FROGO207]

Sadly this is a bad time for trying different propellants if you don't already have them on hand. I am in the try it if you have it category. And find a crony that will be a big help.