Excessive Freebore on 20 Practical??

06x6spdGTO

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Just received 2 NIB barrels from McGowen and measured the OAL to the lands using the Hornady tool before installing them in Aero Receivers.

I am getting a COL length to the lands using the following projectiles.

Speer 39grn TNT - 2.352"
Hornady 45grn SP - 2.314"
Nosler 40grn BT - 2.36"

Both barrels are within .005" of each other.

This seems like excessive freebore considering MAX COL length on 20 TAC data shows 2.245". Anyone else jumping 20 cal bullets .060 - .100" to the lands and achieve 1" or better groups @ 100yd accuracy?

I wrote McGowen back with the measurements in which they sent me a drawing with dimensions of the Pacific Tool Reamer and the following comments:

"The throat reamer will not tell you what distance from ogive is to the lands. And even looking at the SAAMI spec it will give you the minimum. The best way to check is using a dummy round or you can also get one of the chamber gauges that is made from the same piece of material and using the same chambering reamer."
 
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What case did you use? I don't see a Hornady modified case for the 20 practical listed. I have a 20p barrel on order(different manufacturer) and figured I would have to drill and tap a fired case.
 
My McGowan 11 twist Ruger prefit in 20 practical measures 2.235" to lands with 39 Speer tnt's. I don't have any of the other bullets you are trying.
 
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My 11 twist Savage prefit from X-Caliber has 0.025" free bore. They use a JGS reamer.

Using a 32 grain Sierra BlitzKing, I'm 1.9035" to the lands. Using a 34 grain MidwayUSA Dogtown, I'm 1.8725" to the lands. All my measurements are base to ogive (BTO), but looking at targets from load development, I think that puts me at 2.2575" OAL for the Sierra jumping 0.010"; I don't have OAL for the Dogtown noted anywhere.

For what it's worth, I couldn't get the 32 BK's to shoot well in my gun. The Dogtown shot so well - jumping 0.010" - that I just completely gave up on the Sierra bullet and didn't mess with seating depth at all.
 
Originally Posted By: 06x6spdGTOThis is a 1:9 twist 20 Practical but still thinking its reamed to deep in the throat

Since this is a 9 twist barrel I wonder if they throated it deeper for the 55 class of bullets. Not sure but the measurements you are getting seem long.
 
Originally Posted By: tj66Originally Posted By: 06x6spdGTOThis is a 1:9 twist 20 Practical but still thinking its reamed to deep in the throat

Since this is a 9 twist barrel I wonder if they throated it deeper for the 55 class of bullets. Not sure but the measurements you are getting seem long.

9 twist or not I’d still think it’s .075” to deep and could lead to early throat erroision.
 
You just may end up being able to load more powder in the case and get lower pressures. Accuracy could still be amazing.

I have a ton of 5.56 barrels. Ironically the one with the largest chamber/farthest distance to the lands shoots Nosler 55gr BT's into a hole as good as i can hold for. That bullet jumps across the Mississippi river to make the lands.

I have never been more satisfied with a barrel.
 
Originally Posted By: arlaunchYou just may end up being able to load more powder in the case and get lower pressures. Accuracy could still be amazing.

I have a ton of 5.56 barrels. Ironically the one with the largest chamber/farthest distance to the lands shoots Nosler 55gr BT's into a hole as good as i can hold for. That bullet jumps across the Mississippi river to make the lands.

I have never been more satisfied with a barrel.

Got to talk with one of the smiths from
McGowen today. It could be my measuring using the .233 bushed and resized factory Hornady .223 Rem Brass as the neck should be down to the .227 Range. Causing the brass to touch early in the chamber giving a longer length. Regardless McGowen said shoot it. If it’s not accurate send it back with some dummy rounds set at the length you intend to shoot and they’ll make it right.

Gosh dang good customer service and standing behind a product! What more could you ask for!?

So I’ll shoot it this weekend on the 39grn Speer over H335 in some Lake City Brass and see what happens
 
Originally Posted By: spotstalkshootMost accurate measurements come from modified brass shot from barrel you want to measure.

That's why I use a Sinclair tool to get-the real measurements for that chamber and that bullet. Using the case unmodified that was fired in that chamber gives me direct 1:1 data for comparison with quick numbers and repeatability.

Greg
 
Well got it out to try a few loads. Seems to like the 2.20 to 2.22” COL on the 39grn Speer. However that’s the only projectile I’ve tried and over H335 at 23.8grn I’m getting 3450fps 5 shot average using CCI BR4 primers 20” 1:10 twist barrel.

Might try some H4198 at 23.2grn this weekend. Not sure how guys are getting 3600+ and 25.5 gr of H335 as I started seeing pressure signs at 24.1 grn.
 
I load 39 grn Speer. Using CF&E 223 @ 28.0 grs. Chart shows it at 3650 FPS. Also using the Nosler chart for 40gr.Noslers. Using CF&E 223 @ 28.0 grs. I should be getting around 3640 FPS. I used both rounds for coyotes. I prefer the 40gr Noslers Spitzer ballistic tip varmit. 28 grs. CF&E 223 is in the middle of the reloading chart. Charts are on line. Work up your own loads for your rifle.
I reload my 204 Ruger with CF&E 223. Really preforms well in my 1/12 twist rifle.

Rudy
 
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