.308 reform to 7mm-08 case length query

[CCWdownrangeP2]

OK, in anticipation of acquiring a 7mm-08 I've been collecting 308 Win brass to reform to 7mm-08 (much more prevalent case to find). Done about 150 cases so far. The trim to length for 7mm-08 is 2.025". The Hornady cases I've reformed average 2.017", Federal and Winchester 2.020". Should I be concerned about these cases being below the trim to length? If not, how much below the 2.025" is acceptable? Consulted 4 different reloading manuals last night and not one spoke about case length less than the trim to length. To some degree I understand that the shorter neck length will diminish the bearing surface (neck tension) on the bullet. Is there anything else about a shorter neck that should be a concern?

 

[quartermaster]

I wouldn't worry about .005-.008 short. I have fire formed parent cartridges to Ackley Imp and ended up .025 short of the trim to length.

Yours will gain length by shooting them. My Acks didn't gain hardly any length which is understood. I ended up using .280 Rem brass and working it down fire form into the 25-06 AI. It was a .2845 chamber so it took a few steps but my case lengths ended up to be trimmable, therefore worth the effort to me

IMO, go for it. A piece of paper is .004 thick, if that makes you feel better

 

[243winxb]

2.015" saami minimum trim length. http://www.saami.org/specifications_and_information/index.cfm Check loaded rounds neck diameter.

 

[Reloadron]

Should I be concerned about these cases being below the trim to length?

No, what you see in the reloading manual is a "suggested" trim length. If you follow the link that 243winxb was kind enough to provide you will see that the Maximum Cartridge length is 2.035" minus .020" so as 243winxb covers that gets us down to 2.015" as a minimum specification.

There was a time years ago when I resized quite a bit of 308 Winchester to 7mm-08 Remington and never had a problem. One of my concerns was neck thickness and it was never a problem. The only PITA was making sure I kept that ammo separated from my 308 stuff. What I had was 7mm-08 Remington loaded in cases with a 308 Winchester head stamp and rest assured that a 7mm-08 will chamber just fine in a 308 chamber. The bullet has plenty of room as it travels down the barrel with the hot gasses passing it along the way.

Ron

 

[CCWdownrangeP2]

Appreciate the responses. The link to the SAAMI site was excellent, I don't always use all of the resources available to me, thanks. I'll "paint" the heads of the cartridges with Sharpie green to aid in knowing which are the reformed cases. Small step each time I load, but could save a lot of headache. CCW

 

[fguffey]

CCWdownrangeP2, When forming cases I use surplus military cases, my surplus 30/06 cases do not have a head stamp designation. The 7.62 NATO case does not have a head stamp.

When going from 308 W to 7mm08 there is no forming necessary, it is a matter of necking down. I have 308 W forming dies, the forming dies allow me to form 30/06 to 308 W. When forming 7.62 cases for surplus chambers the extra thick case tightens the chamber neck.

F. Guffey

 

[CCWdownrangeP2]

fguffey, Ya, you're right, not so much reforming as just necking down. I do have some mil-surp that are headstamped TW 67, if memory serves me right. Still need a lot more cases as I like to have a minimum of 1,000 rounds of loaded ammo for each cartridge/caliber/gun. I so enjoy learning new things related to reloading!
CCW

 

[AlfieB]

thick necks

I recently aquired a 7mm 08 Mossberg ATR from S.G. for $259. I have been forming cases from FC 308's. I found that at first pass from the FL sizer, the case would not chamber. I then put them back through the sizer 2 more times, and then they work fine. I'm getting sub-MOA groups w/ 46.0 H380.

 

[243winxb]

Case Forming

I found that at first pass from the FL sizer, the case would not chamber. I then put them back through the sizer 2 more times, and then they work fine.

From Lee -

The full length sizing die are not technically a case forming die. There is a certain amount of spring back in the brass case, and this spring back has to be taken into consideration when designing the die and its intended purpose.

Case forming dies usually need to be made to smaller internal dimensions to compensate for more spring back, because the case dimensions are being altered to a greater degree. Sometimes a full length sizing die will work as a case forming die, but it depends on a large number of variables, and is impossible to predict with any accuracy.

Sizing GI 308 to 243 was a problem for me. Full camover with my RCBS press, still left a bolt hard to close.

 

[fguffey]

From Lee -
Quote:
The full length sizing die are not technically a case forming die. There is a certain amount of spring back in the brass case, and this spring back has to be taken into consideration when designing the die and its intended purpose.

Case forming dies usually need to be made to smaller internal dimensions to compensate for more spring back, because the case dimensions are being altered to a greater degree. Sometimes a full length sizing die will work as a case forming die, but it depends on a large number of variables, and is impossible to predict with any accuracy.

Case forming dies usually need to be made to smaller internal dimensions

I am not on a one name bases with any manufacturer, I will assume 'LEE' is the same Lee that manufacturers reloading equipment. If I am correct, lee needs to make sure the person furnishing the information knows what they are talking about.

I have 18 forming dies complete with instructions. It is important the user of the forming die understands the forming die is to be used to form the case and the full length sizing die is to be used to finish the forming process. All of my forming dies are RCBS, all of my instructions insist the case must be sized after forming because the forming die does not completely size the case.

If there was any truth in the quote from Lee all of my forming dies would be small base dies.

F. Guffey

 

[fguffey]

Sizing GI 308 to 243 was a problem for me. Full camover with my RCBS press, still left a bolt hard to close.

This has been discussed before, I have 4 Rock Chuckers, none of my Rock Chuckers cam over. Deductive reasoning, if my Rock Chuckers had the ability to camover I could not use Rock Chucker with my Piggy Back 11 Attachments.

My Rock Chucker rams do kick forward at the top when the linkage goes into a bind. I did grind some metal from the linkage, removing metal from the linkage did allow the Rock Chucker to cam over.

I have no fewer than 10 Herter press, all of my Herter presses cam over. All of my Herter presses are bump presses, when the ram is raised the top of the ram bumps the bottom of the die once on the way up and again on the way down.

F. Guffey

 

[AlfieB]

Lee is correct that there is some spring back when the brass I sized. The resizing a few times tames that problem. It also stands to reason that the case walls get thicker when they are squeezed from 7.92 to 7mm. I guess my question is, how thick should they be?

 

[ironworkerwill]

A good thickness .0115"-.013" **That is unturned PPU brass loaded about 7 times. You know, it gets a fuzz thinner erery time you shoot it...It's not good as Lapua brass either.

 

[Reloadron]

Lee is correct that there is some spring back when the brass I sized. The resizing a few times tames that problem. It also stands to reason that the case walls get thicker when they are squeezed from 7.92 to 7mm. I guess my question is, how thick should they be?

Been there and done that. Ironworkerwill's numbers are pretty much on target.

Remington new unfired 308 Win brass neck thickness, as measured with a micrometer, was on average .013 to .015. That was taking a few measurements on each cartridge.

Remington new unfired 7mm-08 Rem brass neck thickness was about the same with most leaning towards .013 in the lot that I had.

Took some Remington 308 Win brass and ran it through a RCBS 7mm-08 full length sizing die, making sure the cases and necks inside were lubed. On average the 308 to 7-08 really didn't change the brass neck thickness much adding maybe .001" or .002" maximum. The 308 really doesn't change much going from 7.62mm down to 7.00mm.

If you neck 308 down to maybe 243 Win you might see something or need to neck trim but going from 308 to 7-08 I have never seen anything to be concerned with. Not enough to come in light of its intended use anyway.

Ron

 

[AlfieB]

thanks Reloadron and Ironworkerwill. That's a great help. I did mean 7.62.(senior moment).

 

[CCWdownrangeP2]

So far, samples of all I've reformed have chambered just fine in the Savage Axis II that I'm doing all this for. Hopefully will finish a few rounds to try out this weekend.

 

[ironworkerwill]

Just keep shootin that short brass, it'll grow on you.

 

[gwtx]

RED China invented gunpowder. Guns caused climate change. Climate change caused ISIS. RED China should be banned.

+1

 

[CCWdownrangeP2]

^
Huh????

 

[ironworkerwill]

My take on the anti logic... I have a warped sense of humor. BUT, the global warming and IsiS stuff has been reported and repeated by morons all over web.

 

[CCWdownrangeP2]

Still catching up on all the nuances of this thing we call the interweb. I was trying to understand what the statement had to do with the thread, didn't see that as your signature!

 

[fguffey]

Lee is correct that there is some spring back when the brass I sized. The resizing a few times tames that problem. It also stands to reason that the case walls get thicker when they are squeezed from 7.92 to 7mm. I guess my question is, how thick should they be?

It also stands to reason that the case walls get thicker

Then there is measuring before and again after. I have had cases shorten .040” from the end of the neck to the case head when necked up. I do not use the ‘stands to reason’ rational. When I neck a case up the neck gets shorter, when I neck a case neck down it gets longer. And I measure before and again after.

Most reloaders are confused when case forming, necking a neck up and or down is not case forming. Then there is that part about moving the shoulder. Reloaders use the rational of ‘stands to reason’. I find when forming cases my shoulder on the parent case does not move.

F. Guffey