7mm Headspacing Problem

Gents,

Here's a new challenge to think about. I have reloaded for my M70 in 7mm Mag for a number of years now and have never had the problem I'm about to describe. A friend of mine also has a 7mm Mag but in a Remington 700. He's fairly new to rifles and I have been happy to build some bullets for him. But we ran into an issue.

I recently loaded up 20 rounds for him. 16 of those 20 rounds fed no problem, the other 4 however did not feed quite properly. He was able to push the bolt all the way forward but only barely could he close the bolt.

We made some measurements of the brass. We found that the measurement from the case head to the start and end of the shoulder were somewhere around 0.050 - 0.060 inches longer on the rounds that would not feed versus those that would. The overall measurements even for the rounds that would feed were slightly longer than specs in my loading manuals. Not by much, but some. Obviously for the rounds that did not feed, they were quite longer than what would be expected. The OAL for the brass was under the spec of 2.5" for all cases measured.

Now this was on brand new Remington brass which I ran through the FL resizer. For giggles I had some brass waiting to be resized and I ran those through after ensuring the die was setup properly. Same results, it looks like my resizing die is not bumping the shoulder properly.

Do sizing dies wear out? Was the die perhaps just bad to begin with but it took loading for my friend's Remington to find out?

Quite perplexing.

Phil not sure if its your dies or not I've never have had a set of dies wear out before but I replace them every so many years and just sell the old ones on ebay for spare parts, but don't disregard your press as well you didn't state what type of press you were using it could be that its getting old.

Phil,

There are 2 measurements to check to find the source of the problem:

First check the headspacing of the loaded rounds v fired rounds. A stoney point / Hornady head space gauge is very handy for this. Just be sure that you are using the correct insert (0.420") for 7mm. You may find that the headspacing is too long. If so, crank down you sizing die to give you 0.002" bump back of the shoulder from the average you measure on your fired cases.

Second (and more likely if you are on your 3rd, 4th or 5th loading of the brass) is widening of the case just above the belt. Using a caliper or micrometer, measure the diameter of the case just above the belt and compare it to a factory loaded round. Because of the belt, dies for 7mm Rem Mag (and 375 H&H, 300 Win Mag, etc), the die cannot go PAST that point so the area does not resize. The remedy for this is easy, but not cheap: Innovative Technologies makes a special die just for resizing this are of belted mags. The die costs about $90, but works like a charm.

If the base to shoulder measurement cannot be corrected by lowering your sizing die, then it is truly worn out.

If you need a set of RCBS dies, send me PM. I upgraded from RCBS to Redding and retired my RCBS set after loading 350 rounds.

browningbbr

Resizing Belted Magnum Calibers

For shooters that are still wondering how to make your belted cases chamber with 100% reliability, the Innovative Technologies website shows why and how the Belted Magnum Collet Resizing Die works.

It also answers a long list of handloading questions . . . . like why you want to always headspace on the shoulder and not on the belt.

Those .050-.060 of an inch of deviation just can't be. Your cases are being formed in the chamber and would all come out the same. You should be measuring the case that didn't fit before it was fired, not after. Are you positive you're full length resizing? Is the ram on your press slightly camming over when you resize....meaning when the ram goes up is the shell holder touching the bottom of your die with some pressure. When the handle goes all the way down you would feel a very slight bounce just before it bottoms out.

The other thing is, are you using a crimping die or are you inadvertantly over roll crimping your shells during the bullet seating process. If you over crimp you can actually collapse the shoulder ever so slightly to where you wouldn't see it. This would cause the bolt to close very tightly. Be sure to back off your seater die enough so that there is either no crimp or a very slight crimp, if you want it.

Dies don't wear out but you may have a defectve die.

Hope this helps.

I had totally forgot about this thread 1OBH. I actually figured out the problem just recently. The gunsmith at the range I shoot at showed me a trick for FL sizing. Basically you use a lit match to soot up the neck and shoulder of a spent round that was fired in the rifle being reloaded for. You bring the sizing die down to the shell holder but then BACK it out a small amount, not the other way as you'd normally do. Run the brass through the die taking note of where "clean" mark is on the brass.

The first go around the clean mark should be on the neck and not on the shoulder. If there's no mark at all, then you backed out just a bit too much. Ever so slowly you keep screwing the die in until you see the soot just being removed on the shoulder. At this point you take the empty brass and put it in the rifle and see how the bolt closes. If it closes without it being tight, you now set the lock ring on your die. If it's still a bit tight, screw the die in just a very small amount and size the brass again. Once again you check the brass in the rifle. Keep doing this until you find the sweet spot.

What you end up with here is a FL sized brass without creating excessive headspace. This will in turn result in minimizing case stretch and increased brass life. And this is why my 'smith was showing me this.

I took this new lesson and gave it a whirl on brass being sized for my M70 in .300WM. I found out that I just had to barely screw the die in just past the point it contacted the shell holder. If I followed the RCBS instructions to turn the die in 1/8-1/4 turn beyond this point, I'd be bumping the shoulder significantly more than I needed to.

So we tried this on my buddy's Remington. As it turns out if I only turn the die in less than 1/4 turn after touching the shell holder then the brass would be tight on closing, i.e. there wasn't enough headspace. But right at 1/4 turn in, the brass is properly sized.

Bottom line is my buddy's barrel while it was confirmed to be within spec by the gunsmith, it is apparently cut with less headspace then other rifles. We resized 50 rounds this past week, some new brass and others previously shot, and loaded them up. He cycled a bunch of these rounds and all feed properly now.

I regret to inform you but what the gunsmith explained to you is not full length resizing. What he explained is partial resizing. By just touching the shoulder with the die you are only bumping the shoulder back .001-.002 of an inch, which is fine if that ammo is going in the same gun all the time. Every chamber is different and partially resized brass may or may not fit other chambers. I partial resize all the time because it is condusive to increased accuracy, but that ammo is specific to one gun.

Full length resizing on the other hand brings the case back down to SAAMI specifications. So for instance, if you wanted to share ammo with someone or use the same ammo for a few rifles you owned chambered for the same round, you would most likely full length resize.

That match trick the gunsmith showed you is very very old school and was done in the days when there were no bump gauges. If you're serious about reloading this is a cheap enough tool you should own and very simple to use. I use this one from Hornady Hornady Manufacturing Company :: Reloading :: Metallic Reloading :: Tools & Gauges :: Lock-N-Load Gauges-Formerly Stoney Point :: Headspace Gauges :: Headspace Gauge Kits :: Lock-N-Loadï½® Headspace Kit With Body 1 Each

Your buddy has a tight chamber or a chamber very close to spec, that's why he requires full length resized brass...totally fine.

A word of caution...DO NOT partial resize if you're going after dangerous game.

1ObsessedHunter .......

An ordinary Full Length die can set the case shoulder back -.001" if you set die height accurately. The Digital Headspace Gauge helps make this a very easy adjustment, and it works on ALL different calibers without requiring a collection of expensive bushings.

I agree that reliable chambering is never an option. If you use a NK sizing die, keep in mind that rifle cases are tapered and the body also needs some resizing. I designed and patented the Digital Headspace Gauge (and others) that are now used by thousands of shooters.

Innovative said:

1ObsessedHunter .......

An ordinary Full Length die can set the case shoulder back -.001" if you set die height accurately. The Digital Headspace Gauge helps make this a very easy adjustment, and it works on ALL different calibers without requiring a collection of expensive bushings.

I agree that reliable chambering is never an option. If you use a NK sizing die, keep in mind that rifle cases are tapered and the body also needs some resizing. I designed and patented the Digital Headspace Gauge (and others) that are now used by thousands of shooters.

Click to expand...

I quickly jumped on your website...that headspace guage is beautiful. I'll look at your website more in depth over the weekend....thanks

1ObsessedHunter said:

I regret to inform you but what the gunsmith explained to you is not full length resizing. What he explained is partial resizing. By just touching the shoulder with the die you are only bumping the shoulder back .001-.002 of an inch, which is fine if that ammo is going in the same gun all the time. Every chamber is different and partially resized brass may or may not fit other chambers. I partial resize all the time because it is condusive to increased accuracy, but that ammo is specific to one gun.

Full length resizing on the other hand brings the case back down to SAAMI specifications. So for instance, if you wanted to share ammo with someone or use the same ammo for a few rifles you owned chambered for the same round, you would most likely full length resize.

That match trick the gunsmith showed you is very very old school and was done in the days when there were no bump gauges. If you're serious about reloading this is a cheap enough tool you should own and very simple to use. I use this one from Hornady Hornady Manufacturing Company :: Reloading :: Metallic Reloading :: Tools & Gauges :: Lock-N-Load Gauges-Formerly Stoney Point :: Headspace Gauges :: Headspace Gauge Kits :: Lock-N-Loadï½® Headspace Kit With Body 1 Each

Your buddy has a tight chamber or a chamber very close to spec, that's why he requires full length resized brass...totally fine.

A word of caution...DO NOT partial resize if you're going after dangerous game.

Click to expand...

Well technically you're correct, but it's still better than just neck sizing. I do agree with you that this method of sizing is not something to do when loading for DG. You don't want to find out due to temp changes that a round suddenly won't chamber.

I guess what I hope some future reader will get out of this is the somewhat lacking RCBS instructions. 1/8 - 1/4 turn is significant and 1/8 may not be enough. The other side of this is if you go 1/4 and you're reloading for shooting regularly, you may be shortening the life of your brass unnecessarily.

1ObsessedHunter said:

I quickly jumped on your website...that headspace guage is beautiful. I'll look at your website more in depth over the weekend....thanks

Click to expand...

I have that guage and it is indeed a useful tool.