Case sizing

A_a_ron66 · January 22, 2019, 10:47 PM

Alright so I inherited a bunch of .308 brass that had been being reloaded for an AR-10. I have bolt action. 308s and I found out if I didn't get my CL down to about 2.007 the rounds wouldn't chamber in my guns. The brass is starting out around 2.013 give or take so it's a lot to shave off of each case. I guess my question is why are my bolt actions so much more picky than the semi-automatic ARs in regards to case length?

NHSHOOTER · January 23, 2019, 05:02 AM

Upon reading your post I pulled out my Sierra book and checked, "Trim to Length: 2.005". Just a question, have you resized those cases yet?

sparkyv · January 23, 2019, 08:41 AM

Usually, bolt guns have tighter chamber tolerances than semi-autos. This usually results in better accuracy in the bolt gun because of less slop. The additional slop in the semi-auto is intentional so as to improve the reliability if the more rapid feeding of the cartridges.

This response is merely an oversimplified explanation, not intended to be at all comprehensive.

RC20 · January 23, 2019, 01:15 PM

I have one 308 currently and had another one (or a barrel by a different mfg)

Both accepted cases out at the 2.015 limit ( a few got upwards of 2.018 before I caught them and no issues.

What brand 308s do you have and as noted in post 2, is that resized.

Something is not right.

Don Fischer · January 23, 2019, 01:28 PM

There's a reason they put max cartridge length in the reloading manuals!

cw308 · January 23, 2019, 06:28 PM

Your full sizing your brass , then measuring case length? As others have posted the semi chambers are wider so the cases will expand also not just stretch. Keeping your cases trimmed to 2.010 each time would be a good habit to get into . Problem could be base to shoulder length .

Reloadron · January 23, 2019, 06:53 PM

I don't think you want to just focus on the overall cartridge length which according to SAAMI specifications is 2.015" Max -0.020" so anywhere between 1.995" to 2.015", with a suggested Trim To length of 2.005" or about 0.010" below Maximum. You may also want to look at the distance between the case head and the shoulder datum point which is where the shoulder OD is 0.400". That dimension is 1.634" -0.007".

Normally new unfired ammunition will come in right around 1.628 ~ 1.630" and brass fired or sized for a large chamber may be difficult to chamber in a tight chambered bolt gun. I have that issue with my 308 Winchester bolt gun. The chamber is not as particular about the COAL but is particular about the cartridge distance between case head and the shoulder.

Generally I resize using the die instructions and then trim my brass to suggested trim length. Anyway, it's another dimension you may want to consider.

Ron

rox · January 24, 2019, 07:17 AM

Quote:

Originally Posted by Reloadron

I don't think you want to just focus on the overall cartridge length which according to SAAMI specifications is 2.015" Max -0.020" so anywhere between 2.095" to 2.015"

That should be 1.995" to 2.015".

Reloadron · January 24, 2019, 08:43 AM

rox
That should be 1.995" to 2.015".

Thank you. Yep, I sure messed those numbers up. I fixed it.

Ron

locknloader · January 24, 2019, 09:29 AM

While on the topic of 308 cases, i just cleaned and resized some and they were incredibly easy to resize which threw me for a loop. I was using a lee full length sizing die and compared to 223 and pistol cases, it was almost effortless to resize them....

Is this normal for 308 cases? Were they easy to resize because the chamber they were fired in was super tight so they didn't expand as much?

Reloadron · January 24, 2019, 02:54 PM

Some size easily and some offer more resistance. Depends onthe chamber the cases were fired in. I am still for the most part using some RCBS lube in an aerosol spray can which RCBS quit marketing years ago. The lube you use will also figure into how easy or difficult a case sizes.

Ron

RC20 · January 24, 2019, 03:56 PM

And where is our original OP?

Reloadron · January 24, 2019, 05:12 PM

And where is our original OP?

Can we get back to you on that?

Ron

RC20 · January 24, 2019, 07:50 PM

Yes you can, just don't make me hold my breath.

January 22, 2019, 10:47 PM	#1
A_a_ron66 Junior Member Join Date: January 21, 2019 Posts: 1	Case sizing Alright so I inherited a bunch of .308 brass that had been being reloaded for an AR-10. I have bolt action. 308s and I found out if I didn't get my CL down to about 2.007 the rounds wouldn't chamber in my guns. The brass is starting out around 2.013 give or take so it's a lot to shave off of each case. I guess my question is why are my bolt actions so much more picky than the semi-automatic ARs in regards to case length?

January 23, 2019, 08:41 AM	#3
sparkyv Senior Member Join Date: May 2, 2015 Location: Deepinnaheartta,Texas Posts: 189	Usually, bolt guns have tighter chamber tolerances than semi-autos. This usually results in better accuracy in the bolt gun because of less slop. The additional slop in the semi-auto is intentional so as to improve the reliability if the more rapid feeding of the cartridges. This response is merely an oversimplified explanation, not intended to be at all comprehensive. __________________ μολὼν λαβέ NRA Life Member

January 23, 2019, 01:15 PM	#4
RC20 Senior Member Join Date: April 10, 2008 Location: Alaska Posts: 6,220	I have one 308 currently and had another one (or a barrel by a different mfg) Both accepted cases out at the 2.015 limit ( a few got upwards of 2.018 before I caught them and no issues. What brand 308s do you have and as noted in post 2, is that resized. Something is not right. __________________ Science and Facts are True whether you believe it or not

January 23, 2019, 06:53 PM	#7
Reloadron Senior Member Join Date: June 8, 2016 Location: Cleveland, Ohio Suburbs Posts: 1,424	I don't think you want to just focus on the overall cartridge length which according to SAAMI specifications is 2.015" Max -0.020" so anywhere between 1.995" to 2.015", with a suggested Trim To length of 2.005" or about 0.010" below Maximum. You may also want to look at the distance between the case head and the shoulder datum point which is where the shoulder OD is 0.400". That dimension is 1.634" -0.007". Normally new unfired ammunition will come in right around 1.628 ~ 1.630" and brass fired or sized for a large chamber may be difficult to chamber in a tight chambered bolt gun. I have that issue with my 308 Winchester bolt gun. The chamber is not as particular about the COAL but is particular about the cartridge distance between case head and the shoulder. Generally I resize using the die instructions and then trim my brass to suggested trim length. Anyway, it's another dimension you may want to consider. Ron Last edited by Reloadron; January 24, 2019 at 08:44 AM.

January 24, 2019, 03:56 PM	#12
RC20 Senior Member Join Date: April 10, 2008 Location: Alaska Posts: 6,220	And where is our original OP? __________________ Science and Facts are True whether you believe it or not

January 23, 2019, 05:02 AM	#2
NHSHOOTER Senior Member Join Date: November 26, 2012 Location: Concord NH Posts: 876	Upon reading your post I pulled out my Sierra book and checked, "Trim to Length: 2.005". Just a question, have you resized those cases yet?

January 23, 2019, 01:28 PM	#5
Don Fischer Senior Member Join Date: March 2, 2017 Posts: 1,615	There's a reason they put max cartridge length in the reloading manuals!

January 23, 2019, 06:28 PM	#6
cw308 Senior Member Join Date: September 2, 2010 Location: Plainview , Long Island NY Posts: 3,675	Your full sizing your brass , then measuring case length? As others have posted the semi chambers are wider so the cases will expand also not just stretch. Keeping your cases trimmed to 2.010 each time would be a good habit to get into . Problem could be base to shoulder length .

January 24, 2019, 08:43 AM	#9
Reloadron Senior Member Join Date: June 8, 2016 Location: Cleveland, Ohio Suburbs Posts: 1,424	rox That should be 1.995" to 2.015". Thank you. Yep, I sure messed those numbers up. I fixed it. Ron

January 24, 2019, 09:29 AM	#10
locknloader Senior Member Join Date: August 28, 2017 Posts: 164	While on the topic of 308 cases, i just cleaned and resized some and they were incredibly easy to resize which threw me for a loop. I was using a lee full length sizing die and compared to 223 and pistol cases, it was almost effortless to resize them.... Is this normal for 308 cases? Were they easy to resize because the chamber they were fired in was super tight so they didn't expand as much?

January 24, 2019, 02:54 PM	#11
Reloadron Senior Member Join Date: June 8, 2016 Location: Cleveland, Ohio Suburbs Posts: 1,424	Some size easily and some offer more resistance. Depends onthe chamber the cases were fired in. I am still for the most part using some RCBS lube in an aerosol spray can which RCBS quit marketing years ago. The lube you use will also figure into how easy or difficult a case sizes. Ron

January 24, 2019, 05:12 PM	#13
Reloadron Senior Member Join Date: June 8, 2016 Location: Cleveland, Ohio Suburbs Posts: 1,424	And where is our original OP? Can we get back to you on that? Ron

January 24, 2019, 07:50 PM	#14
RC20 Senior Member Join Date: April 10, 2008 Location: Alaska Posts: 6,220	Yes you can, just don't make me hold my breath. __________________ Science and Facts are True whether you believe it or not

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