10mm. Worth converting from .40?

4

45Colt

New member
I have a para P16-40 SS with a Limited slide that is a great gun, but has terrible accuracy. I have not seen many other .40s that shoot gnats @$$ accuracy, either. 'Course my problem just may be because I load both lead and jacketed in the mid-range of recommended powder charges. (BTW I also have a P14-45 that shoots unbelieveably accurately no matter what I feed it.) So, 'cause I'm always looking to improve what I already have, I'm thinking about doing a conversion to 10mm with a Bar-Sto or Kart barrel, and a heavy duty recoil spring. Now I need some expert advice from those of you who have been .45 shooters and who have made the move to 10mm:
Can the 10mm be as accurate as a .45?
Would loading up the .40 to a max charge to approximate the 10mm improve the effectiveness of the round? (I note in Speer's manual that there isn't much difference between the .40 and the 10mm with same weight bullets)
Is it really worth all the trouble to make the conversion?
Thanks, in advance, for your thoughts
45Colt
 
I think you just need to work up a better load. Inacuracy in a 1911 is due to loosness in the bushing and barrel/slide lock up. If the gun is tight then you need a better load. If you buy new parts and they don't fit good your accuracy won't be any better. A .40 is a short 10mm for all intents. A good gunsmith can rechamber your .40 barrel and put in a heavier spring if you want to shoot 10mm. Para mags will hold the longer 10mm cartridge. For high end loads the 10mm case is stronger and can handle higher pressure. If your gun is tight I would work on a better load. Ask the IPSC limited shooters what kinds of loads they shoot for a good starting point.
 
I have been contemplating getting a P16 for just such a conversion .40S&W to 10mm. A conversion is as *easy* as a barrel change (BarSto, Ed Brown and Jarvis), heavier recoil spring and the +10% mag springs for reliability. How can you argue with 16+1 (or 18 with the bumpers! :D) rounds of 10mm firepower?

Now some folks have had horrid accuracy problems with the .40S&W. My two most accurate .40s are my Walther P99 and my Browning (that long sight radius really helps). Both of these pistols are about as accurate as any of my other pistols (I don't do a lot of sandbag shooting, so I have never tried a true out and out test of the most accurate pistol).

Now if you look at the specs of the two rounds and do some math, there is a difference. The 10mm Auto is a true .400" round. The .40S&W is actually .4005" round.

Now the case taper is from .424 to .423 in the .40S&W and in the 10mm Auto the taper is .425 to .423. Mathematically that works out to .400" even for the 10mm and .4005" for the .40S&W.

Does that matter? I dunno, but it sure seems like a good excuse for poor shooting on my part! How's that saying go? It is a poor musician who blames his instrument? :D

Derek
 
Regarding if it's worth it to go from .40S&W to 10mm...

On the caliber front, the 10mm can be loaded to much higher power levels much more safely than .40S&W. A hot 155gr .40S&W load is in the neighborhood of 1175-1205 FPS. A hot 155gr 10mm load is 1350-1400 FPS. Put another way, while you are struggling to get .40 S&W over 500 ft-lbs, the 10mm can be pushed to 670+ ft-lbs (like Cor-Bon's 180gr JSP) without any drama. Since the 10mm brass is also much stronger than the .40S&W brass you also have a greater margin for error.

10mm guns can be extremely accurate but I'm not sure how much of your problem comes down to load/gun-specific issues as opposed to the alleged inferiority of .40S&W itself.

C.B.
 
When I bought my Delta Elite last year, the tag read "easy conversion to .40 S&W IPSC gun!" HA! The 1911 action is designed for a cartridge of 10mm/.45 length; notice how many IPSC guys load their .40's out to almost 10mm OAL? Because the pressures are lower and the guns are more reliable that way. Why not just go all the way to truth, and make it a 10? The only reason that I see for a 1911-pattern in .40 is the availability of cheap brass. Changing the chambering of your gun will not necessarily make it any more accurate, but if you are going to get a new barrel, etc. anyway, then it's the perfect opportunity to change it to 10mm. On the other hand, if your gun is for IPSC gaming, the .40 is perfectly capable of meeting the new, watered-down power factor. I've loaded sub-minor rounds with N320 and some screamers with AA #7; the gun likes them all (with a spring change for the weak ones). I don't shoot my 10 as well as my .45, but that's more the factory sights and trigger on the 10, than any deficiency in the gun.
 
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