Does lapping in the locking lugs on bolt increase head space

[JackF]

Hammer,

At first thought that last statement would seem correct. However, thinking more on it, I would think that the extractor would be made to actually travel a little beyond the rim to account for different shoulder to rim and or different belt to rim lengths as not all cases are made to the exact same specs. As for the brass case being too soft you are probably right. I was hoping I could detect the added effort to lock the bolt when the bolt hit the screw. If all else fails I will look in my brass bin and see if I have a piece of round stock I could machine to mimic a once fired case. This is something I was trying to avoid.

Jack.

P.S. We missed you at the Gears show today.

[Harold_V]

I will look in my brass bin and see if I have a piece of round stock I could machine to mimic a once fired case. This is something I was trying to avoid.

It would be my opinion that that wouldn't yield the desired results. It's virtually impossible for you to duplicate the chamber in the same way form firing does. I'd suggest you stick with a once fired case, which most likely will be the best representation of the bore and current headspace. If you encounter issues with the extractor, it can be removed temporarily while determinations are made.

P.S. We missed you at the Gears show today.

Yep! I had hopes of meeting you. Wish you could have made it.

We did manage to meet a couple others, which made the day quite enjoyable. It's nice to be able to put a face on a name we see daily.

Some very nice models of engines were presented for all to enjoy, and who wouldn't enjoy the opportunity to stand under the beautiful Daylight (SP 4449).

Harold

edit:

[JackF]

Harold forgot to mention the two beautiful brass cannons at the show.

Jack.

[Harold_V]

Harold forgot to mention the two beautiful brass cannons at the show.

Jack.

You mean these?
Beautiful workmanship!
The carriages were made of walnut.

Harold

[JackF]

Dat be dem. You are quick on the pics.

Jack.

[GeorgeGaskill]

Getting back to the headspace discussion, , it is always best to entirely strip the bolt of all parts when testing for headspace as the process requires a lot of feel and the mainspring and ejector springs dramatically interfere with the feel to the extent of making the measurements unreliable. You want to be able to feel the least resistance to closing the bolt on the gauge, not whether you can force the bolt closed or not.

I an not an advocate of using cartridge cases for headspace measurement (although others are) because of at least two reasons. Number one is that you do not know what the actual dimensions of any given cartridge case is. They have tolerances just like any mass produced product and if they will allow the bolt to be closed, most manufacturers consider them OK. Neither of these characteristics make a good gauge. Number two is the cartridge is too springy. The once fired cases will get a little smaller once the chamber pressure is released and this leads to it being a little shorter than the actual chamber. This also leads to questions about actual measurements although it is not as bad as the tolerance issue.

Since the standard headspace gauges for belted cases are buttons that measure the belt depth, you would not be getting a shoulder to breech distance using them, assuming that is the distance you really want to know. It would be useful in measuring the increase in headspace you get from the bolt lapping process, however.

[JackF]

Thanks George for the reply. From my readings I understand that most ammo manufactures form there cases so the shoulder falls a bit short of the chamber shoulder thus when the cartridge is fired it will stretch and move the shoulder forward to fill the chamber shoulder. This is the reason I will first try to use a fired case from the gun I will be reloading for. Thanks for suggesting the bolt should be striped for the test. I will do that. It will be some time however before I am able to test or lap the lugs as there are many more urgent chores on my list before that happens.

Jack.

[GlennW]

Thanks George for the reply. From my readings I understand that most ammo manufactures form there cases so the shoulder falls a bit short of the chamber shoulder thus when the cartridge is fired it will stretch and move the shoulder forward to fill the chamber shoulder.

Not a gun guy, but wouldn't that defeat the purpose of what you are trying to accomplish?

Won't the present head space become a factor in how much the cartridge shoulder expands?

Seems like a catch 22!

[JackF]

Hi Glenn,

I'm not really a gun(smith) guy myself but trying to get into it so am doing a lot of reading and "You Tubing". The 300 Win Mag is a belted case and from what I can gather, because in the factory loads the shoulder is a bit short of the chamber shoulder the belt registers the cartridge in the chamber for the first firing. At that time the case will expand and move the shoulder forward to fit the chamber shoulder. If I read correctly, the case from the belt rearward will also stretch some toward the bolt face, I suspect however, very little. The once fired case now, if care is taken to not move the shoulder back during resizing, will register with the belt and shoulder. Some "expert?" reloaders say if full length sizing be sure to stop just short of pushing the shoulder back, others say to neck size only. In any case I feel the once fired cases should "move" very little between loads and will give me the best indication of my actual head space. Some guys to measure head space use a fired case and add measured shims or tape stuck to the back of the case until they feel resistance to the bolt closing or until the bolt will not close. One fellow I watched on You Tube claims he wants .000 to .005 head space. When I get to actually measuring my head space I will I will follow George's advice and strip the bolt so as to have nothing but the bolt face causing resistance. I suspect it will take a lot of experimenting to nail this all down and it will be a learning experience.

Sorry for the long post.

Jack

[unioncreek]

Headspace on a belted round is always on the front of the belt and never on the shoulder. I would either takea factory loade round or a resized case and use scotch stape on the base. First measure the thickness of the tape with a micrometer not a caliper. Put some tape on the base trim it round with a knife and try it keep adding till the bolt will not close. I always shoot for .002 when chambering a barrel to be the most accurate.

Bob

[GeorgeGaskill]

Belted case headspace gauges are trivial to make; they are simple cylinders .532-.533" in diameter and .212" to .220" in length. You could make yourself a set in .001" increments if you have a surface grinder.

I do not recommend the use of cartridge cases for measuring headspace, even though others do, because you do not know the dimensions of the case you are using (unless you have some way of accurately measuring it such as a shadowgraph.) Because of the simplicity of the gauges, I would make myself a set from O-1 or W-1 drill rod. Harden if you like but you likely won't use them enough to get any appreciable wear.

Use the proper tool.

[JackF]

Thanks for the suggestions George and Bob. I haven't made any head space gages yet for lack of time but I did try the tape on the end of a fired case method. My tape measured .0015. With 1 tape there was no resistance, with 2 tapes I was able to detect some resistance, with 3 tapes the bolt would not close. This tells me, as much as the tape test is able to, that I have more than .0015 but just less than .003 head space. The trouble with any test gage, be it store bought, home made, or once fired cases is that the actual cases I will be reloading vary in the measurement from the front of the belt to the rear of the case from .215 to .217. This is between cases of the same brand and fired in my gun. I also have some unfired off shore ammo with the same .215 to .217. To confuse things even further I bought some once fired(?) range cases that vary from .212 to .216. Because of these variances between cases I feel the best way to get actual head space measurements is by using cases fired in my gun. There is so much to learn.

Jack.