Normal Headspace Expansion? - 300 WSM

[P_Mo80]

I'm beginning to work on load development for a 300 wsm

Using Hornady Headspace Comparator

UNFIRED brass headspace measurement: 2.260
Fired Brass (once fired) measurement: 2.283

Question 1: Is 23 thousands expansion normal? Seems like a lot.

Question 2: This is a belted magnum, am I ok measuring headspace (using the comparator set) from the base of the cartridge? I've read a couple things indicating that it should be measured from the belt. Would love to hear your thoughts on both of those.

Thanks in advance!

 

[Steel head]

300 WSM has a belt?
.023 is a lot, if it has a belt and the belt is holding base reasonably close to the bolt face it’s a lot less of an issue.
Pics of you cartridges???

 

[Eric_F]

300 WSM doesn't have a belt, headspaces off the shoulder. 300 Win Mag does have a belt that it headspaces off of, but that still sounds like a ton. Have you checked your fired cases inside with a paperclip to see if there is case head separation starting?

 

[MtnCreek]

I assume this is a Win Mag, correct?

Assuming win mag, you should disregard the belt and set up the die as you would for a non-belted cartridge.

 

[P_Mo80]

GOOD GRIEF!!! 300 Win Mag ... not WSM. Sorry for inadvertently subjecting you guys to some top shelf A**Hat-ery! Win mag .

I measured belt to base on a fired case ... looks like about 2 thousands expansion. (measured with digital caliper by hand ... so "about" ..)
I'll check it with a paper clip to make sure nothing is going on inside the case.

 

[FLIGHT762]

Like MtnCreek posted, fire the new brass and then set you die to F/L bump the shoulder datum -.002" for you rifle's chamber.

 

[918v]

23 thou is normal both mine do about that.

 

[Steel head]

GOOD GRIEF!!! 300 Win Mag ... not WSM. Sorry for inadvertently subjecting you guys to some top shelf A**Hat-ery! Win mag .

I measured belt to base on a fired case ... looks like about 2 thousands expansion. (measured with digital caliper by hand ... so "about" ..)
I'll check it with a paper clip to make sure nothing is going on inside the case.

If the case expands with the base against the bolt face the shoulder tends to blow out instead of the case stretching.
It’s seems pretty common for belted mags to stretch a lot but as long as the belt is doing it’s job it a non issue.
Now you can just bump the shoulder back a few thou like normal.

 

[Deleted member 10043]

I'm beginning to work on load development for a 300 wsm

Using Hornady Headspace Comparator

UNFIRED brass headspace measurement: 2.260
Fired Brass (once fired) measurement: 2.283

Question 1: Is 23 thousands expansion normal? Seems like a lot.

Question 2: This is a belted magnum, am I ok measuring headspace (using the comparator set) from the base of the cartridge? I've read a couple things indicating that it should be measured from the belt. Would love to hear your thoughts on both of those.

Thanks in advance!

Only the H&H is measured from the belt.

 

[Deleted member 10043]

If the case expands with the base against the bolt face the shoulder tends to blow out instead of the case stretching.
It’s seems pretty common for belted mags to stretch a lot but as long as the belt is doing it’s job it a non issue.
Now you can just bump the shoulder back a few thou like normal.

The belt isn't doing anything. It has no job on the 300 WM or any other mag except the H&H. The belt is just there to look cool, lol.

 

[Steel head]

The belt isn't doing anything. It has no job on the 300 WM or any other mag except the H&H. The belt is just there to look cool, lol.

Actually the belt does have an important purpose and it’s not just to look pretty.

 

[Cr1775]

The belt isn't doing anything. It has no job on the 300 WM or any other mag except the H&H. The belt is just there to look cool, lol.

What 300 WM if its like a 7RM it headspaces off the belt and i believe that to be correct it aint there to look cool thats alot of jump but my 7mm has alot of jump not by my bench now so cant see my notes

 

[Cr1775]

But good topic how do you measure headspace with a belted mag i ended up giving a guy my brass and he took it to work and he was sblt to get me the measurements from in frount of the belt

 

[Deleted member 10043]

True, but not common on more modern mags due to sharp angled shoulders rather than what you see on the H&H. Seriously, research the development from the H&H on up to today. You'll see where I'm coming from and there is lineage. On the 300 WM the belt may add a little undeisigned support on very hot loads but unlike the H&H bulging the web area on a WM is not a good sign.

 

[Deleted member 10043]

Actually the belt does have an important purpose and it’s not just to look pretty.

Enlighten me.

 

[Deleted member 10043]

Never mind. I found a nice article and read the whole thing. There is a little middle ground though. But this statement is where I'm coming from.

"Most every other cartridge that features the H&H style belt will use the shoulder for headspace, and the belt on this style case is non-functional."

Redirect Notice

BTW, I have a 300 H&H build for precision shooting so I have some experience with the cartridge that started it all. The 300 WM has a couple hundred fps over it and is easier to reload. But it is no way more accurate.

 

[918v]

When you have .023” of shoulder clearance on many factory chambers, the belt is functional. But for reloading purposes you can just ignore it.

 

[Deleted member 10043]

When you have .023” of shoulder clearance on many factory chambers, the belt is functional. But for reloading purposes you can just ignore it.

Can you explain further?

 

[918v]

If you spun the case in a lathe and turned off the belt, you would get headspace separation in a chamber with .023” shoulder clearance.

The belt keeps the case head against the bolt face for that first firing.

 

[bmash]

On my 7 mm mag the first firing case growth is a lot! (I’m not at home so I can’t give amount) When I full length sized, after about three firings the case had a noticeable internal groove above the belt. (You an catch this with a paper clip.) As several already recommended above, after the first firing just bump the shoulder. Brass life is much improved.

 

[Deleted member 10043]

If you spun the case in a lathe and turned off the belt, you would get headspace separation in a chamber with .023” shoulder clearance.

The belt keeps the case head against the bolt face for that first firing.

But it still has to stretch and now you're into excessive case streching regardless. Is .023 SAAMI spec?

 

[Deleted member 10043]

On my 7 mm mag the first firing case growth is a lot! (I’m not at home so I can’t give amount) When I full length sized, after about three firings the case had a noticeable internal groove above the belt. (You an catch this with a paper clip.) As several already recommended above, after the first firing just bump the shoulder. Brass life is much improved.

That is not good. Again is your chamber within specs. I'm still not convinced the belt is making up for out of spec chambering. If it is its not supposed to and that is not good. Plenty of other mags without belts firing under similar conditions leading to the same sort of premature brass failure.

 

[Steel head]

Enlighten me.

On the important first firing or if shoulder is pushed back excessively on sizing the belt does the same thing as if you made a false shoulder or jammed the bullet when blowing out a wildcat, holding the base against the bolt face.

Hence the case sides are not getting stretched and promoting case head separations.

 

[bmash]

That is not good. Again is your chamber within specs. I'm still not convinced the belt is making up for out of spec chambering. If it is its not supposed to and that is not good. Plenty of other mags without belts firing under similar conditions leading to the same sort of premature brass failure.

What do mean by “not good”? Accuracy? dangerous? For a match rifle? Hunting rifle? For brass?
This is on a 1980s Winchester model 70 with factory barrel. It is very accurate with close to max reloads and has been used to killed many deer, so it is “good” for me. In spec chamber? I really dont know and sure don’t plan to rebarrel due to this. It is safe based on 35 plus years of shooting. (no pressure signs or other issues.) It works great and as long as I bump the shoulder when sizing brass life is no problem. My next door neighbor told me about this issue many years ago as he had the same experience. I guess his rifle is out of spec as well...
I will admit my bumped shoulder brass will not come close to fitting in my sons or bil’s rifles, so I do have a very “generous” chamber and I have often wondered if it were “in spec”. It sure doesn’t affect accuracy based on results in this rifle. Based on the chamber I would have to bet it is head spacing on the belt, because it isn’t close to the shoulder. It will be middle of the week before I get home but I’ll look at my case measurements and compare to spec. You have peaked my interest.
thanks!

 

[Cr1775]

What do mean by “not good”? Accuracy? dangerous? For a match rifle? Hunting rifle? For brass?
This is on a 1980s Winchester model 70 with factory barrel. It is very accurate with close to max reloads and has been used to killed many deer, so it is “good” for me. In spec chamber? I really dont know and sure don’t plan to rebarrel due to this. It is safe based on 35 plus years of shooting. (no pressure signs or other issues.) It works great and as long as I bump the shoulder when sizing brass life is no problem. My next door neighbor told me about this issue many years ago as he had the same experience. I guess his rifle is out of spec as well...
I will admit my bumped shoulder brass will not come close to fitting in my sons or bil’s rifles, so I do have a very “generous” chamber and I have often wondered if it were “in spec”. It sure doesn’t affect accuracy based on results in this rifle. Based on the chamber I would have to bet it is head spacing on the belt, because it isn’t close to the shoulder. It will be middle of the week before I get home but I’ll look at my case measurements and compare to spec. You have peaked my interest.
thanks!

 

[918v]

But it still has to stretch and now you're into excessive case streching regardless. Is .023 SAAMI spec?

I dunno if it’s saami spec. My rifles are built to cip spec.

The brass I pick up from other rifles is much shorter, something like .005-.008” shorter. Still too much for my liking.

But to answer your question, the .023” case length growth when headspacing off the belt does not thin out the case walls like it would if it were headspacing off the shoulder. The mechanism is completely different. If you section a once fired 300WM case you won’t find any visible signs of case wall thinning. But take any non belted case and bump the shoulder back .023” and fire it, then section the case. You’ll see a case either separated or about to.

 

[Cr1775]

I guess your rirle is junk you should sell it to me ill give you 100 for it no i would not worry about it just resize accordingly and we will be fine my 7mm also has an excessive growth as well and im at my 6th reload on the brass

 

[Deleted member 10043]

There are no material differences between CIP and SAAMI specs for the 300 Win Mag. What is different are brass manufacturers and case capacity. So, we still don't know if the chamber specs should be .023 longer than the cartridge specs.

@bmash You said after three firings you are getting indications of brass separation. That is what I mean by not good under any circumstances. If anybody is clearly depending soley on the belt from preventing case head separation than it is an indirect benefit outside of manufacturer specifications. Your particular rifle has seen a lot of use but what you describe is a problem, regardless. It is okay so long as you don't have to rely on brass that has been reloaded more than a few times from what I gather.

 

[Deleted member 10043]

On the important first firing or if shoulder is pushed back excessively on sizing the belt does the same thing as if you made a false shoulder or jammed the bullet when blowing out a wildcat, holding the base against the bolt face.

Hence the case sides are not getting stretched and promoting case head separations.

Yes, I pretty much said never mind on my very next post with that short article.

 

[Steel head]

Yes, I pretty much said never mind on my very next post with that short article.

I think your in shock from too much muzzle break concussion, I told you that muzzle brakes would dumb you down eventually.

 

[bmash]

There are no material differences between CIP and SAAMI specs for the 300 Win Mag. What is different are brass manufacturers and case capacity. So, we still don't know if the chamber specs should be .023 longer than the cartridge specs.

@bmash You said after three firings you are getting indications of brass separation. That is what I mean by not good under any circumstances. If anybody is clearly depending soley on the belt from preventing case head separation than it is an indirect benefit outside of manufacturer specifications. Your particular rifle has seen a lot of use but what you describe is a problem, regardless. It is okay so long as you don't have to rely on brass that has been reloaded more than a few times.

Sorry if I didn’t communicate well. I WAS getting signs of separation - not when I bump the shoulder. When I full length resized it was a problem. But this is why I said bump the shoulder. Hence, no problem. My brass lasts a long time now. If this were a high round count match rifle I would rebarrel. Regardless I am not going to waste money rebarrelling a very accurate hunting rifle...

 

[Deleted member 10043]

300 WM

 

[918v]

There are no material differences between CIP and SAAMI specs for the 300 Win Mag. What is different are brass manufacturers and case capacity. So, we still don't know if the chamber specs should be .023 longer than the cartridge specs.

Manufacturers do their own thing. My rifles are from the same manufacturer (Sako) about 10 years apart. I have picked up brass from other rifles that is as long as mine. So it’s not just Sako.

In any case, judging by most of the brass I pick up, I’d guess on average factory chambers allow the brass to grow .010-.015”. My chambers are huge, but I don’t have pressure issues and my brass lasts 10-15 reloads. I have a lot of free brass and I have formed brass from .300 H&H Magnum cases. The H&H formed brass lasts longer as I have full control over headspace. And I end up with a 50 thousands longer neck instead of that short nub.

 

[Deleted member 10043]

I think your in shock from too much muzzle break concussion, I told you that muzzle brakes would dumb you down eventually.

For Krist's sake and for Veer, RIP, please proofread your posts.

 

[Steel head]

For Krist's sake and for Veer, RIP, please proofread your posts.

Lol
Proof reedin is for dem smart city folk.