300 win mag headspace
- Thread starter 806guns
- Start date
mike mccormick
Silver $$ Contributor
No. Set headspace with the belted go gage as you would any other.
The 300 win.mg. head spaces off the belt. The draw back of this is that most cases stretch appox.15 to 18 thousands before shoulder of case head space off shoulder of case. This can cause case head separation after several reloading. So if you reload,don't push shoulder back until 2nd or 3rd firing, then only 3 thousand.
mike mccormick
Silver $$ Contributor
Exactly. We are discussing setting barrel headspace. Not reloading practices.
I see there is a few tips on reloading 300 wm as well. I will be doing this too. But buying a box or two of factory ammo first
L.Sherm
Silver $$ Contributor
Go to there website I cant remember for sure but I think it cuts it about in half.
The Peterson long brass is approx 10 thousands more than normal 300 mg..this should put you approx 5 to 8 thousands short of shoulder touching chamber.
JamesinAsheville
Silver $$ Contributor
I size my brass to headspace off the shoulder and no problems
The 300 Win Mag is a “belt and suspenders” cartidge. I don’t process that brass any differently, in F-Class use.
The belt was originally to stop old-style straight wall cases from moving forward.
However the Win Mag obviously has the bottleneck cartidge shoulder to stop that motion.
Thus, it fire-forms like any modern cartridge we use and is absolutely guaranteed to not move forward.
The belt is more than vestigial. In theory, a belted cartridge where the belt hard-stops against the recess cut into the chamber should eliminate ignition inconsistency possible when regular cartridges vary slightly from each other in a combination of set back, body taper or length, following the same rationale for why we seat primers where they “stop” as opposed to just flush with the head.
The belt was originally to stop old-style straight wall cases from moving forward.
However the Win Mag obviously has the bottleneck cartidge shoulder to stop that motion.
Thus, it fire-forms like any modern cartridge we use and is absolutely guaranteed to not move forward.
The belt is more than vestigial. In theory, a belted cartridge where the belt hard-stops against the recess cut into the chamber should eliminate ignition inconsistency possible when regular cartridges vary slightly from each other in a combination of set back, body taper or length, following the same rationale for why we seat primers where they “stop” as opposed to just flush with the head.
Last edited:
Nominal minimum headspace for a belted cartridge is .220". Standard practice is to cut the chamber to .222', allowing .002" for compression when the barrel is tightened. This for a hunting rifle which you want to feed and function every time. Now, the measurement from the base to the front of the belt on most belted cases is usually from .212" to .216". This means you will have head clearance of from .004 to.008. While this isn't ideal, it will allow the shoulder to blow forward and produce a case with no clearance.
One can cut the chamber a little tight, but I would not want to cut to any less than .218. While it seems unlikely you will find brass longer in headspace than that, it could happen. To end up at .218, I cut .220 and count on compression to give me the final dimension.
Since you are just screwing on a Remage, you will tighten to contact firmly on the .220 gauge then lock the nut. You should end up at .221 or so. WH
One can cut the chamber a little tight, but I would not want to cut to any less than .218. While it seems unlikely you will find brass longer in headspace than that, it could happen. To end up at .218, I cut .220 and count on compression to give me the final dimension.
Since you are just screwing on a Remage, you will tighten to contact firmly on the .220 gauge then lock the nut. You should end up at .221 or so. WH
Not sure how to accurately measure this. As I'm use to using the comparator.
WSnyder
Silver $$ Contributor
If you roll your own barrels.
Take one of your cases and turn the belt off of it. Fill case with epoxy. Now you have a custom headspace gage.
Short chamber barrel to fit your case gage +.002” or whatever clearance you like.
Use a boring bar to cut/deepen belt recess to your brass +.002” or whatever clearance you like.
Now you have a belted mag chamber to fit your brass. If you bought enough brass to start with you can kill the barrel with that batch. If you ever want to sell the thing run the reamer in to depth using a std belted mag headspace gage for headspace.
Take one of your cases and turn the belt off of it. Fill case with epoxy. Now you have a custom headspace gage.
Short chamber barrel to fit your case gage +.002” or whatever clearance you like.
Use a boring bar to cut/deepen belt recess to your brass +.002” or whatever clearance you like.
Now you have a belted mag chamber to fit your brass. If you bought enough brass to start with you can kill the barrel with that batch. If you ever want to sell the thing run the reamer in to depth using a std belted mag headspace gage for headspace.
I do not. Just seeing if this is normal or excessive
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.