7mm mag case trim length - just general hunting up to 400 yards max

[CamaroMan]

Hi all- kinda wondering, the 7mm mag case trim length, max length is at 2.5" - checked afew fired rounds here and they are all exactly at 2.5 after being fired (tikka t3x)..

I was trimming back to 2.490-2.495 (almost 200 rounds now with no adverse issues) - but wondering if i could just stick with 2.495 and trim less every time?

Havent had a single round stick or give issues on both me and the wifes rifles (both t3x's) and so far accuracy has been pretty darn accurate.

thanks

 

[Phil Rizzo]

If they chamber easily in your gun after resizing, I say keep going. Sometimes when you look at a chambered case with a borescope you find there is more room also, for cases longer than SAAMI spec.

 

[Bucklowery]

If it is working go for it. It is a tolerance and you are in it

Thanks

Buck

 

[Reelamin]

I seldom trim brass and never really had adverse results. 3-5 shots before I even check is my norm, and then I worry more about uniformity than OAL and what the book/internet says I must be at. Edit...I will add.....the more exact and detailed the better your results will be just document the details that led to what your results are.

 

[CamaroMan]

thanks - yes no issues so far. I wonder if they have a spec so the rounds will not jam in all makes of rifles - thanks currently running around 2.495.

 

[cdherman]

I seldom trim brass and never really had adverse results. 3-5 shots before I even check is my norm, and then I worry more about uniformity than OAL and what the book/internet says I must be at. Edit...I will add.....the more exact and detailed the better your results will be just document the details that led to what your results are.

If you are not full length resizing, but just bumping the shoulder, you will seldom need to trim. I almost forget to check anymore, and seeing a couple threads on the topic today reminds me to not forget.

Remember, the downside to a long case is FAR worse than the cartridge not chambering. It MAY chamber with a little resistance that you miss, pushing the neck of the case into the throat, and turning the brass down into the bullet. In essence crimping, BUT its not a reversible crimp.

You pull the trigger and if you are LUCKY, you just blow the primer. Unlucky and you lose an eye or a finger, or part of your jaw.......

 

[can1010]

chamber 2.524
case 2.500
trim 2.490
your pretty safe at 2.495 more important to be consistent at whatever length you choose.

 

[Mikecr]

You should just measure your chamber length, so that you'll know what your max trim length actually is.
Otherwise, you have no idea, and neither does anyone else.
Good tool for this: https://www.brownells.com/reloading/measuring-tools/case-length-gauges/sinclair-chamber-length-gage/

 

[bamban]

Delete

 

[can1010]

the Brownells chamber length gauge is ok but is dependent on one neck dia. and chamfer angle change either one of them and the measurement will be different. the only sure way is checking with a bore scope but for the average person just stick with the book specs and be safe.
the measurement on the print provided is 2.524.

 

[Mikecr]

the Brownells chamber length gauge is ok but is dependent on one neck dia. and chamfer angle change either one of them and the measurement will be different. the only sure way is checking with a bore scope but for the average person just stick with the book specs and be safe.
the measurement on the print provided is 2.524.

If I understand you correctly, you're thinking that a chamber neck diameter might be so big as to cause the gauge slug to contact somewhere up on chamber end 45deg angle. But that much clearance would allow the slug to contact a chamber end edge. That is, there would be enough clearance to prevent centering, while desired in this case. You could use a bore scope to confirm that, and perhaps trial & error wiggle/rechamber the case until achieving it for a good measure.

Bottom line though, if you want to know your actual chamber length, you have to measure it.
It's not in a book or SAAMI drawing.
If you just trim to a book value or standard drawing, you will not know your chamber end clearance.
Chamber end clearance, like any clearance, is important beyond mere safety.

 

[FEENIX]

thanks - yes no issues so far. I wonder if they have a spec so the rounds will not jam in all makes of rifles - thanks currently running around 2.495.

Don't complicate it unnecessarily.

chamber 2.524
case 2.500
trim 2.490
your pretty safe at 2.495 more important to be consistent at whatever length you choose.

This!

 

[can1010]

If I understand you correctly, you're thinking that a chamber neck diameter might be so big as to cause the gauge slug to contact somewhere up on chamber end 45deg angle. But that much clearance would allow the slug to contact a chamber end edge. That is, there would be enough clearance to prevent centering, while desired in this case. You could use a bore scope to confirm that, and perhaps trial & error wiggle/rechamber the case until achieving it for a good measure.

Bottom line though, if you want to know your actual chamber length, you have to measure it.
It's not in a book or SAAMI drawing.
If you just trim to a book value or standard drawing, you will not know your chamber end clearance.
Chamber end clearance, like any clearance, is important beyond mere safety.

agreed that the only way to know exact length is to measure it but the Brownell gauge isn't the best for the average loader. i have them and the dia. of the gauge is between .004-.008 smaller than the chamber giving you a longer length than actual length that is why the recommend in directions to subtract .020 off your measurement and then you are close enough to saami length to just use that. the advantage of knowing and going long is to eliminate room for a carbon ring to form and a little extra neck length.

 

[Dmagna]

Take a bore scope and see how much room you have when you chamber a piece of brass.