Freeboring/Throating your .40S&W Barrel

[Hagop]

What truly are the advantages of freeboring your barrel?

Is there any significant loss of accuracy in doing so?

What type of pistol should you consider doing this modification to?

After you have freebored/throated your barrel should you be deterred from firing factory ammo through it in exceptional cases?

Does freeboring/throating your barrel cause expanding gases to be bled past the case flamming it and erroding the breechface prematurely?

[ErikW]

What truly are the advantages of freeboring your barrel?

You can use longer ammunition, in part to aid feeding, and in part to lower pressure and perhaps make it softer shooting.

Is there any significant loss of accuracy in doing so?

I can't answer that, not having tested the same gun freebored and not freebored. But revolvers are still accurate with a big jump into the forcing cone and rifling.

What type of pistol should you consider doing this modification to?

One that you want to load to Major power factor, and for which magazines accept longer rounds. Which is to say, 1911 designs, and not others.

After you have freebored/throated your barrel should you be deterred from firing factory ammo through it in exceptional cases?

No.

Does freeboring/throating your barrel cause expanding gases to be bled past the case flamming it and erroding the breechface prematurely?

No.

[bountyhunter]

I only polish the throat on barrels that are too tight and don't feed factory ammo correctly.  With a lot of 1911's they come new with this problem because polishing the ramp and throat are hand operations and they just aren't done at the factory for cost savings.  Be advised to do the absolute minimum polishing in the thraot (especially on .40's) as you don't want to remove any more than is necessary.

[grassy knoll]

isn't it necessary for 200 gr bullets in a .40?

[Flexmoney]

Your current barrel may have more "freebore" than you realize.

Test by loading some dummy rounds long and see what will fit.  (you may want to mark/blacken the bullets so that you can see any "witness marks" from when they touch)

[DougCarden]

In my nowlin bbl. 40 I was able to load 180 lfp, 200gr lfp, etc. to 1.180.  I,  however, have a buttload of Clays and wanted to run that and a longer OAL.  I had my bbl. reamed for 1.200, and never looked back.  Best $20 bucks I spent, no problems whatsoever, and my Clays loads with Fed small pistol primers look just fine, much better than my .38 special 230gr pinloads!(primers that is).  Most guys around me just load to 1.180 and run 231 or a similar powder.  I have to be different.  DougC

[ErikW]

I'd like to see Brazos Custom chime in on this topic so you can get the opinion of a professional gunsmith.

[Brazos Custom]

Glad to help Erik,

Some freebore is necessary if you are going to load long for the 40 cal.  Factory OAL is 1.135 most IPSC shooters are loading 1.18-1.25.  If you don't freebore a little the longer loads will cause excess pressure.  I have done testing to see if accuracy is affected.  The results were that in all cases there was no deterioration in accuracy and in some cases the accuracy of the gun improved significantly. The freebore acts similar to the forcing cone in a revolver - if your bullet is slightly misaligned it will gently force it back to the center. In the early days I had a special reamer made that was 0.403 diam. but most of the reamers I have seen lately from clymer seem to be cutting enough freebore in the chamber.  If you have an older reamer or an STI/SV more than a couple of years old you might need to do something.  It has not been a problem in the barrels I have checked lately.  Most IPSC pistolsmiths have figured out that you need the freebore and most of them are cutting the barrels appropriately. Easiest way to check is to look in the chamber with a flashlight you should be able to see about 0.2 inch of freebore before the rifling starts.

[DBChaffin]

Thanks for the great post Bob.

I add this only because of coincidence, but I was reading the instructions that come with a Schuemann barrel last night, and they included a recommendation for .2 inch of freebore and stated that it would not adversely affect accuracy at all.  Getting that exact number as the approximation from Bob above makes it seem even more accurate.

[benos]

Thanks Bob!

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