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.270Win Chamber too small

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Unread 09-14-2009, 11:16 AM
Junior Member
Join Date: Sep 2009
Posts: 14
.270Win Chamber too small

Hi Guys,

I've been reloading for my new .270Win for a short while now and get acceptable groups from the bench over 100m. Last week I obtained a RBCS precision mic to determine my rifles headspace. The mic. works on the principle of measuring fired brass from your rifle (thus fire-formed in your chamber) which closely (approx. -0.002') resembles your chamber size..

The manual also supplies the ANSI min and max. values for a specific cartrigde (refering to the length from the head of the case to a datum point on the shoulder). I'm not sure as I don't have the manual with me now, but I think the tolerances are min: 2.0487' ; max: 2.0587' for the .270Win.
The "zero" reading on the mic refer to the minimum ANSI spec. nl. 2.0487'

Now for my problem: Fired Brass from my rifle gives a measurement of -0.0025' (avg. of 25 fired cases measured). This equals
2.0487' - 0.0025' = 2.0462' , which is below the ANSI min. value. Even if I allow 0.002' for the "springback" effect of the cases, this still means that my chamber is slightly too small.

Handbooks suggested that I should resize to 0.001' - 0.002' more than the actual headspace (2.048'), but when I set my full length resizing die (hornady) to max (shell holder touching the base of the resizing die) these cases grew in lenght by 0.004' to +0.002' (measurement in the precision mic was now 2.051') Although these rounds do chamber in my rifle, a little bit of force is need too close the bolt.

Should I :
1) Only neck size?
2) take a few thousands of an inch off the base of the full lenght resizing die,
to allow the case to move "deeper" into the die in order to set the shoulder
back to -0.002' off the headspace?
3) Have the chamber of my rifle enlarged by a few thou of an inch?
4) Just continue reloading as current ( thus, will this slightly oversized cases
for my chamber influence my accuracy/safety?)

Hope you can give some advise.

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Unread 09-14-2009, 11:32 AM
Platinum Member
Join Date: Jan 2004
Location: Blackfoot, Idaho
Posts: 8,876
Re: .270Win Chamber too small

I just did a big long reply but had one of them there epiphanies towards the tail end of it.

What about shaving a couple of thou off of the top of the shell holder?

If this works it would be the most simple and straight forward, I would think.
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Unread 09-14-2009, 06:14 PM
Silver Member
Join Date: Mar 2002
Location: Casselberry, FL
Posts: 192
Re: .270Win Chamber too small

Namibia .........

Whatever you do, don't shave down your shellholder (or your die). I see this done about once a week, and it never helps anyone. Here's why; die manufacturers design their FL resizing dies to make handloads small enough to fit in even the smallest chamber in any given caliber, and the tolerances for modern dies are very accurate.

You need to understand your RCBS Precision Mic to get accurate measurements. Keep in mind that you're only interested in the "difference" between your fireformed case and your handloads. You'll probably get the most consistent readings if you remove the primer in every case that you measure (just don't resize your fireformed case).

You should not be able to "feel" your handloads chamber - not even a little bit. The only two possible reasons for your cases fitting too tight . . . . . . is they're either too long (at the shoulder), or they're too wide (about .500" above the base).

You should be able to determine which is your problem length (at the shoulder) or width above the web of your cases. Our Digital Headspace Gauge works the same way comparing your handloads to your fireformed case. Unlike the RCBS Precision Mic it's a bit easier to use, and it works on ALL different calibers.

- Innovative
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Unread 09-14-2009, 06:37 PM
Silver Member
Join Date: Jan 2005
Posts: 262
Re: .270Win Chamber too small

I agree that I wouldn't like a casing that chambers with even a little effort in my guns for hunting.
I DO NOT agree with Larry...although I like him and use some of his products...that it is a bad idea to take about .010" off that shellholder. I have several sets of hornady dies and although I like some features about them their tolerances have sometimes been such that I had to shave a shellholder to make the m work properly. The top of the shellholder HAS NO FUNCTION for any normal reloading procedure and it's the cheapest tool to modify and easiest.
Go for it. I'll bet a 12 pack with Larry it fixes your problem.....I've seen plenty of other posts where this has been whats needed also.
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Unread 09-14-2009, 07:18 PM
Platinum Member
Join Date: Feb 2008
Posts: 1,002
Re: .270Win Chamber too small

I wouldn't touch the shellholder or die base.
If you neck size only, eventually you'll need to FL size anyway!

The reason your brass is hard to chamber after sizing is because it's being lengthened in the die and the shoulder isn't being pushed back, this lengthens the case by squeezing the case walls in and pushing brass forward into the shoulder and neck. Brass is reluctant to take reshaping, it actually springs back inside the die just as it does in the chamber when fired, you need to bump it past the point required, and let it spring back to the desired dimensions. The force required is staggering! The amount of spring back is equally staggering!

The easiest way to 'bump' your shoulder back is to screw the die in until it touches the shellholder, then raise the press handle and screw it in a further 1/8 turn so it cams over on the top stroke of the press handle, make adjustments in small increments (1/32 turns) until you get the desired measurement from the precision mic. Once set, lock everything up, and you'll be set for the life of that rifle.

If the shellholder is only touching the die base when you raise the ram, it will NOT be touching the die base with a case installed, it must be touching the die base when actually sizing a case for it to work correctly!

I have a minium chamber in my 25-06, and I have to have it cam over quite a bit to get .002" below the fireformed case dimensions, this is what the precision mic is for. My chamber is 2.050", I resize back to 2.048" using the precision mic to determine exact headspace, no other tool is required to do this.

Your FL die can quite easily go beyond minimum dimensions, that is what 'oversizing' your brass is, reducing headspace too much.
If you follow the above procedure, you'll get precise fitting of your resized cases to your chamber.
It is not a problem having a minimum chamber, because brass life is extended substantially by not stretching the cases excessively during fireforming, then from fireformed condition to resized condition the brass is being 'worked' the absolute minimum, it is actually a good thing!
Hope this helps you get the desired results.
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Unread 09-15-2009, 03:01 AM
Silver Member
Join Date: Jan 2005
Posts: 262
Re: .270Win Chamber too small

Excellent response! I had ASSumed he had already gotten into slightly camming over and you are certainly right that you can pick up a few thousanths by doing so. If he does as you describe it should certainly work out as he almost has it sizing enough now.
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Unread 09-15-2009, 04:08 AM
Silver Member
Join Date: Dec 2008
Location: Spokane WA.
Posts: 228
Re: .270Win Chamber too small

I would get your lugs lapped.
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