Bolt Vs Gas Gun Reloading

kraigwy · February 8, 2009, 08:13 PM

I mentioned several times about the differance between loading for gas guns vs. bolt guns, mainly the requirment for full lengh resizing, making sure the shoulder is set back propertly.

As we know, (or should know) when the gas gun is fired, the gas starts openning the bolt before the bullet leaves the barrel, this causes two, opisite effects on the brass. The gas starts pushing the bolt back, pulling on the rim, while the gas pressure is still pushing on the inside of the shoulder. This causes the shoulder to be pushed beyond what neck sizing will fix, ending up with excessive case lengh (shoulder to rim) of the case. When the shoulder isnt set back to specs it can cause: Failure to feed, failure to extract, or in worse cases slam fires. The slam fires are not as much as issue with ARs as they are with M1s and M14/M1As.

Below are some messurements I did on my guns.

For 223, I used my Rem 700 V bolt gun and a tight chambered WOA Upper for the gas gun. Resulting case lengh are as follows:

Bolt gun = 1.759, Gas gun = 1.778 or .021 differance

For 308, I used a Rem 700 Target rifle and my Super Match M1A,

Bolt gun 2.024 gas gun = 2.031 or a differance in .007

For the 06, I used a Vietnam Era Sniper rifle replica Model 70 and my NM M1

Bolt gun 2.488, gas gun = 2.539 or a .061 differance.

If you compair the differance between the two guns to the No - No -Go respective headspace gages you can see you have a problem.

If the gun's headspace is excessive (to a point) you can still shoot it safely but accuracy will suffer. If the case headspace is excessive, you run into the problem of the firearm firing while not tataly in battery causing the problems listed above.

I have seen match directors carry case lenth gages to the firing line and check suspected reloads removing excessive lengh rounds from the firing line. I do that myself.

Case gages are cheap, and should be used in setting up sizing dies. Small base dies arnt enough, they size the base of the case but do nothing for the shoulder to rim lengh. There are several makes of gages, the ones I use (pictured below) are the Wilson gages for the 223 & 308 and my homemade gage in 30.06.

The differaces I listed above are in my guns, all of which (except the M1) have tight target chambers. Your guns will very, depending on the chamber. I believe this is why people recommend against using MG Brass for reloading. MG are more violent in the action of extracting rounds and do stretch more, but they can be reloaded IF the cases are sized to specs.

bigalshootmupper · February 8, 2009, 11:22 PM

Great post Kraig.
For reference, my DPMS LR308 has a chamber that measures -0.002 headspace from SAMMI spec according to my RCBS precision mic. Measurements of my brass is 2.025 after firing. They save you should trim each case after each firing for gas guns. I may be able to get away with doing it every other firing - but I will measure each one after resizing to make sure not too long. I don't have a check gauge yet, using calipers. Any recommendations on a good cheap gauge? How much for Wilson gauges?

baugh55grfmj · February 15, 2009, 08:51 PM

Interesting....Finally I get the answer I'm lookin for. Same problem with my AR. I went from a lee full length die to a CH small base die and it fixed the problem.

Striker1 · February 15, 2009, 09:27 PM

I too use the LE Wilson gages but it isn't that easy to tell if the rim is between the "High and Low mark". Is the Dillon easier to read?

Thanks

February 8, 2009, 08:13 PM	#1
kraigwy Senior Member Join Date: June 16, 2008 Location: Wyoming Posts: 8,618	Bolt Vs Gas Gun Reloading I mentioned several times about the differance between loading for gas guns vs. bolt guns, mainly the requirment for full lengh resizing, making sure the shoulder is set back propertly. As we know, (or should know) when the gas gun is fired, the gas starts openning the bolt before the bullet leaves the barrel, this causes two, opisite effects on the brass. The gas starts pushing the bolt back, pulling on the rim, while the gas pressure is still pushing on the inside of the shoulder. This causes the shoulder to be pushed beyond what neck sizing will fix, ending up with excessive case lengh (shoulder to rim) of the case. When the shoulder isnt set back to specs it can cause: Failure to feed, failure to extract, or in worse cases slam fires. The slam fires are not as much as issue with ARs as they are with M1s and M14/M1As. Below are some messurements I did on my guns. For 223, I used my Rem 700 V bolt gun and a tight chambered WOA Upper for the gas gun. Resulting case lengh are as follows: Bolt gun = 1.759, Gas gun = 1.778 or .021 differance For 308, I used a Rem 700 Target rifle and my Super Match M1A, Bolt gun 2.024 gas gun = 2.031 or a differance in .007 For the 06, I used a Vietnam Era Sniper rifle replica Model 70 and my NM M1 Bolt gun 2.488, gas gun = 2.539 or a .061 differance. If you compair the differance between the two guns to the No - No -Go respective headspace gages you can see you have a problem. If the gun's headspace is excessive (to a point) you can still shoot it safely but accuracy will suffer. If the case headspace is excessive, you run into the problem of the firearm firing while not tataly in battery causing the problems listed above. I have seen match directors carry case lenth gages to the firing line and check suspected reloads removing excessive lengh rounds from the firing line. I do that myself. Case gages are cheap, and should be used in setting up sizing dies. Small base dies arnt enough, they size the base of the case but do nothing for the shoulder to rim lengh. There are several makes of gages, the ones I use (pictured below) are the Wilson gages for the 223 & 308 and my homemade gage in 30.06. The differaces I listed above are in my guns, all of which (except the M1) have tight target chambers. Your guns will very, depending on the chamber. I believe this is why people recommend against using MG Brass for reloading. MG are more violent in the action of extracting rounds and do stretch more, but they can be reloaded IF the cases are sized to specs. __________________ Kraig Stuart CPT USAR Ret USAMU Sniper School Oct '78 Distinguished Rifle Badge 1071

February 8, 2009, 11:22 PM	#2
bigalshootmupper Senior Member Join Date: November 21, 2008 Location: Georgia Posts: 146	Great post Kraig. For reference, my DPMS LR308 has a chamber that measures -0.002 headspace from SAMMI spec according to my RCBS precision mic. Measurements of my brass is 2.025 after firing. They save you should trim each case after each firing for gas guns. I may be able to get away with doing it every other firing - but I will measure each one after resizing to make sure not too long. I don't have a check gauge yet, using calipers. Any recommendations on a good cheap gauge? How much for Wilson gauges? __________________ ”If you want to find out what is wrong with your country, go look in the mirror.” Ross Perot

February 15, 2009, 08:51 PM	#3
baugh55grfmj Junior Member Join Date: February 14, 2009 Posts: 3	Interesting....Finally I get the answer I'm lookin for. Same problem with my AR. I went from a lee full length die to a CH small base die and it fixed the problem.

February 15, 2009, 09:27 PM	#4
Striker1 Senior Member Join Date: May 22, 2004 Location: TX Posts: 550	I too use the LE Wilson gages but it isn't that easy to tell if the rim is between the "High and Low mark". Is the Dillon easier to read? Thanks