Low pressure powders for semi auto’s

davide montini

davide montini

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Low pressure powders for semi auto’s

Hello all
To the more experienced loaders out there ...can you shine some light on this
What’s the deal with semi’s and loading with low pressure powders...looking at the burn rate chart and determine what to use...for example a fnh fnar semi 308 or a browning bar or a Springfield m1a1 ...and say either 155,,168,,175 grain bullets....
How does one judge or got about this ....trying to figure it out ......and at the same time not beating the living hell out of the semi’s or damaging them
Thanks for the response and help on this
Davide
 
They can all make high pressure if you load them hot enough. But I know where your thought process is on this one. Looking at the burn rate chart then the load data and trying to come up with the magic recipe.
All I can suggest is the method that I've "worked up". There, I just said it. Start your loads low then work your way up. Either in .3 or .5 grain increments with your ladder testing, then tune from there.
I load currently for an xcr-l, xcr-m, ar's, sks. Have had .223 bulpups that came before my ar's that were the test bed for loads. As well as an m305.
You'll know when it gets too hot, believe me. Super snappy, hard cycling action and my favorite... barrel harmonics similar to a dull ringing bell sound (don't get to that point).
 
When I'm loading low pressure loads for the 308 I usually just go with 4831. Don't have any load data on me at the moment but generally you can fill the case all the way up with a 155 grain bullet and still be ok, that's been my experience anyway. You should check out a loading manual before trying anything new to you as they'll usually have the pressures listed and just to be safe. I have a chart of relative burn rates for powders up in my reloading area and I can't speak for much on how one goes about figuring it all out, I think with time you just get to "know" how a lot of different powders operate in certain cartridges and with different bullet weights. Maybe try out a few of the slower powders and see what you find out. Here is a useful online manual that includes pressure data: http://www.hodgdonreloading.com/data/rifle

I haven't used any of my 308 loads in a semi-auto but Hodgdon recommends using these powders for military duplicate loads in the 308 so they might be worth checking out for you. Maybe start with the lowest recommended amount of powder and bump it down in half a grain increments until it starts to feel a little gentler:

BL-C(2)
IMR 4895
H4895
Varget
IMR 4064
 
The issue is not pressure in the usual sense - chamber pressure in the 50,000 to 60,000 psi

The issue is port pressure. If the pressure is too high at the gas port it beats up the system. The solution is a faster powder, so that the pressure has dropped more by the time the bullet passes the gas port.

In 308, something in the 4895 speed range. If you go slower - say Varget - don't load as hot as usual.

Don't use a slow powder like 4350.
 
Ok ..to start off I have lots of books you name it I got it (probably)....I’m steady comparing loads loaded ...and the max psi....for the loads ....I have found some similar things ....and as I suspected they are loading with 24” barrels ...some shorter 22.....
And all bolt action .....only 2 books say for m14 types guns.....so for powders ...to load with faster powders in the burn rate ...they won’t do any harm to the actions of a semi....like Imr 3031...benchmark ......from what I’ve been reading. They all say nothing slower than imr 4064......
Holy cow this can get expensive!!!....powder and bullets Jesus h a#d&$s....
And then buy the time one is done doing there load testing....barrel might be garbage!!!!!
I thank you to all that have responded.....and it’s nice to hear what other say and to learn from others
I had a guy ask me what I was shooting I told him my load and bullet
Lapua brass...cci 34..""varget ..41.4 grain...155.5 Berger bullits ...crony at 2525fps.....
Fnh fnar 20” heavy barrel
He said I should be up around 2600+ fps......
Believe me I tried but the pressure signs were there ...on brass....gun was jumping and kicking hard .....
So this is why I’m talking on here to get some insight
Thank you all and I have enjoyed this journey....see you on the firing line
 
You should be able to send it faster. Military 147gr ammo goes at roughly 2800 FPS from a 22'' barrel. A crater on the primer can also be because of a long firing pin and/or large gap around it on the bolt face. Look for flattened primers and extractor marks.
 
You do not want to use Varget... the faster powders will serve you better. Port pressure and gas volume is why you are beating the rifle up.

If you have access to an adjustable gas block, get one... that will help alot to tone down your rig.

Jerry
 
When I load for an m1 garand I use 48 gn of IMR 4064. It's a weaker load and still performs well in the gun without beating it up
Every semi auto is different so you have to expirement a bit with powder charge
In my mg 34 when I shoot 308 I use 4064 and I have been using 4350 in the 8x57, the gun seems to perform better with the 308 so I want to do some expiramenting with 4064 in the 8mm
 
In addition to my previous post, my pet load in my semi auto .308's is 42.2 gr imr 4895 pushing 150 gr hornady fmjbt's.

Accurate enough over various platforms and cycles all actions without beating them up.p
 
I've been shooting 42gr of either of the 4895s behind a 150gr Hornady FMJ. This is with thicker NATO cases.
It's a great M80 spec load. Getting about 2750fps with some overlap between IMR and Hodgdon 4895. Quite accurate in the 22" M14.
 
And to all of you who have replied....no problems with the action...not damaging anything....and still nolding accuracy ....good solid reliable accuracy out to long distances say like over 50p...600 meter plus
Please let me know
 
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