7mm advice

[stapleen]

Hey guys. I am getting ready to build a 7mm long range rifle. I have had the barrel on order for some time, and krieger's estimated delivery was in July, but it looks like it just shipped yesterday, so I guess I better get with the program deciding what caliber to build. I initially was going to build a 7mm mag, but I don't care for the problems I have experienced in the past with this caliber. I am referring to the amount of stretch this case seems to have upon initial firing with new brass and a chamber headspaced off the belt. My question is, will I still end up with this same scenario in a 7mm stw chambering? Does the available 7mm stw brass on the market stretch as much as the 7mm mag does initially? I have no problems with the 7mm mag once that initial firing is completed and I then start headspacing off the shoulder. I just don't like the wasted step of initially firing new brass. The little experience I have with this, it produced a less than acceptable accuracy in my opinion. Any insight would be appreciated.

Thanks

 

[MudRunner2005]

I've never had any issues with a 7mm RemMag...And I've had 4 of them (still have 3, cause 1 got stolen). Anyway, sounds to me like someone was drunk when they cut that chamber, or they used a FUBAR'd reamer that was WAY out of spec. You shouldn't hate a caliber based on a faulty chamber.

Anyway, any smith worth his salt should be able to cut a chamber with a good reamer to perfect spec, and not over-headspace it like your 7mm RemMag.

I think you will like the 7mm STW. And it is a great LR monster with the big 180gr bullets.

 

[stapleen]

Mudrunner, thank you for the response. This chamber is cut to spec. This is a Rem Sendero in 7mm mag. I once thought what you did when I first tried to reload for this rifle. A headspace measurement taken with a Hornady headspace gauge on new Rem unfired brass was x measurement. A once fired piece of brass measured with the same gauge was now x+.018". My group size was around an inch at 100 yards. I took all the once fired brass and full length sized it using a Redding .015" over shellholder, thus bumping the shoulder back .003", and my group size decreased to 3/8". I thought I had some sort of screwed up chamber, so instead of being smart and researching this scenario, I took the rifle apart and recut a 7mm rem mag saami spec chamber in this barrel with a brand new pt&g reamer. Guess what I found when I put it back together. You guessed it, the exact same condition. I have since researched this on the internet and this problem seems common amongst 7mm mag owners.

My question is not whether or not this condition exists, its whether or not this condition also exists in a 7mm stw.

 

[MudRunner2005]

That's strange, I've never had this issue with any of mine. Never had that issue with my 7mm STW either.

 

[Lefty7mmstw]

A good way to stop that initial stretch out on a belted is to create a false shoulder by necking a caliber up and then coming back down to your caliber with your dies set up to barely chamber the round. My current stw has a bit of a generous chamber (even with a custom bbl.), but with properly set dies you can still get a bunch of firings out of your brass; I do.

 

[Engineering101]

stapleen

Sounds like you have learned the hard way. Take a look at the 7mm WSM. No belt. Pretty much duplicates the Rem Mag. I'm running the 180 Bergers at 2,950 fps and grouping around 1 inch at 200 yards out of a 26" 4 groove Brux. I get a slightly sticky bolt about one out of 10 rounds so I figure to be right at max load with 69.8 grains of Magnum. The WSM family of cases hold several national accuracy records at 1,000 yards so accuracy potential is first rate. The one caveat is that only Winchester makes brass for the 7mm WSM and it can be hard to come by. On the other had there are many who make 270 WSM brass which can be fire formed up to the slightly longer 7mm WSM.

 

[stapleen]

A good way to stop that initial stretch out on a belted is to create a false shoulder by necking a caliber up and then coming back down to your caliber with your dies set up to barely chamber the round. My current stw has a bit of a generous chamber (even with a custom bbl.), but with properly set dies you can still get a bunch of firings out of your brass; I do.

I was doing some reading and I saw where someone was forming 300 win mag brass to 7mm brass. With properly set dies, this gentlemen claimed to achieve a shoulder headspace custom to his chamber. It was an old post so I can't just ask him about it. Have you ever heard of doing this and what dies would you need?

 

[stapleen]

stapleen

Sounds like you have learned the hard way. Take a look at the 7mm WSM. No belt. Pretty much duplicates the Rem Mag. I'm running the 180 Bergers at 2,950 fps and grouping around 1 inch at 200 yards out of a 26" 4 groove Brux. I get a slightly sticky bolt about one out of 10 rounds so I figure to be right at max load with 69.8 grains of Magnum. The WSM family of cases hold several national accuracy records at 1,000 yards so accuracy potential is first rate. The one caveat is that only Winchester makes brass for the 7mm WSM and it can be hard to come by. On the other had there are many who make 270 WSM brass which can be fire formed up to the slightly longer 7mm WSM.

Are there any feeding issues from an internal magazine with these cartridges?

 

[stapleen]

That's strange, I've never had this issue with any of mine. Never had that issue with my 7mm STW either.

I don't know if I would have ever noticed such a scenario if I wasn't taking some precise measurements before and after firings of my cartridges. The brass shows no physical signs what-so-ever. I just always try to set up my rifle dies to slightly bump the shoulder back every time, so I measure before and after and set my die accordingly. Some guys neck size after initial firing, I full length size every time, but as minimally as possible.

 

[Edd]

Build a 7mm-26 Nosler. PTG has the reamer listed on their website. That will give you 7 STW case capacity and no belt.

 

[MudRunner2005]

I don't know if I would have ever noticed such a scenario if I wasn't taking some precise measurements before and after firings of my cartridges. The brass shows no physical signs what-so-ever. I just always try to set up my rifle dies to slightly bump the shoulder back every time, so I measure before and after and set my die accordingly. Some guys neck size after initial firing, I full length size every time, but as minimally as possible.

I know my .25-06 Ackley & .30-06 Ackley brass shrinks the neck .0200" when fire-forming. But my belted .300 Ackley Improved Magnum pushes the brass forward when it forms the shoulder, because it headspaces off the belt.

With belted cartridges it doesn't hurt anything for the cases to expand forward during fire-forming, it's what they're designed to do.

Personally, I wouldn't own a short magnum, unless it was the wildcat 6.5 SS (Sherman Shortmag). But that involves a whole lot of forming and brass prep work.

I personally wouldn't worry too much about .018" stretch unless that stretch starts showing the signs of a case/head separation. But that's just me.

I also think most new brass stretches alot more than most people realize. Remember, it has to be small enough to fit in everyone's gun world-wide. They have to leave wiggle-room so that it will work with no issues.

Have you tried comparing a new piece of brass and measuring it next to a SAAMI spec printout of the 7mm RemMag case dimensions? I bet the new brass will be significantly smaller.

 

[stapleen]

I know my .25-06 Ackley & .30-06 Ackley brass shrinks the neck .0200" when fire-forming. But my belted .300 Ackley Improved Magnum pushes the brass forward when it forms the shoulder, because it headspaces off the belt.

With belted cartridges it doesn't hurt anything for the cases to expand forward during fire-forming, it's what they're designed to do.

Personally, I wouldn't own a short magnum, unless it was the wildcat 6.5 SS (Sherman Shortmag). But that involves a whole lot of forming and brass prep work.

I personally wouldn't worry too much about .018" stretch unless that stretch starts showing the signs of a case/head separation. But that's just me.

I also think most new brass stretches alot more than most people realize. Remember, it has to be small enough to fit in everyone's gun world-wide. They have to leave wiggle-room so that it will work with no issues.

Have you tried comparing a new piece of brass and measuring it next to a SAAMI spec printout of the 7mm RemMag case dimensions? I bet the new brass will be significantly smaller.

I am not worried about the case stretch of this caliber causing a problem. If the initial loading of new brass produced a 3/8" group like the once fired brass does, I wouldn't care if it stretched a mile as long as it didn't seperate, but it produces a 1" inch group instead. That is not acceptable to me for what I am wanting to achieve.

 

[stapleen]

Build a 7mm-26 Nosler. PTG has the reamer listed on their website. That will give you 7 STW case capacity and no belt.

I hadn't thought of that. I will research it a little bit. Thank you.

 

[dakor]

I have seen the problem you are talking about in various belted magnums. Easy solution is just neck size and not full length size. Another option is have a reamer built to the specs you would like the brass to blow out to and use that to chamber your rifle. If you are going to go to a non belted case the cheapest and easiest route would be the 7mm Ultra mag. If you do not like that option look at a 7mm-338 Norma mag or 7mm-338 Lapua.