An NoR reader asked a fairly common question this morning: What kind of velocity and energy increases will I see from a pistol caliber carbine over a standard pistol.
I'm a BIG advocate of pistol caliber carbines, especially if you have a companion piece for them , but people don't generally understand their performance characteristics, so lets take a look at them.
Typically speaking, with a loading that can use it (slower burning powder or heavy loads), you’ll see a 40% or so velocity increase between a 16” rifle barrel and a 5” pistol test barrel (about 3.75” actual rifled barrel length because the test barrel is measured from the breech face. Also note, real pistol barrels are NOT test barrels). Then add 25-50 fps per inch after that until the point of diminishing returns (which is highly variable).
Remember, this is for handloads using slower burning large magnum powders, which can effectively use the barrel length. Standard pistol loads wont see nearly as large an increase.
The first example I want to use is a .357 revolver and a .357 lever action carbine.
We're going to review test barrel numbers, so it's important to remember a new 4” revolver barrel with a tight cylinder gap will typically see 25-50fps less than a 5” test barrel. An older revolver will typically see between 50-100fps less as the forcing cone wears. Also newer revolvers seem to get better velocity out of the same barrel lengths than older revolvers (more comparable to test barrels); which seems to be a manufacturing process issue.
Now, to our examples.
Buffalo Bore lists their 125gr hot load as 1600fps from a new 4” S&W mountain gun, and 2310fps for an 18.5” marlin 1894, which matches up with those approximations reasonably well.
1625fps * 1.4 = 2275fps + (62.5-125 fps for barrel length adjustment) = 2335 - 2397fps
Remember, every gun and every bullet will have different rifling characteristics, different bore smoothness, different bearing surfaces on the bullet etc… so there are some wide variations.
Looking at hot and/or heavy .357 loads from Buffalo Bore and DoubleTap ammo you see the following
Doubletap from pistol test barrel:
(all doubletap ammo listed here is from a 4” SP101 and will be adjusted using the above approximation)
125gr at 1650fps - 755 ftlbs
158gr at 1350fps - 640 ftlbs
Doubletap projected from 20” rifle (assuming a 40% increase over a 5” test barrel, and 25fps per inch over 16")
125gr at 2410fps - 1611ftlbs
158gr at 1990fps - 1390ftlbs
Buffalo Bore from 5” test barrel:
125gr at 1700fps - 800ftlbs
158gr at 1475fps - 765ftlbs
170gr at 1400fps - 740ftlbs
180gr at 1400fps - 785ftlbs
Buffalo Bore projected from 20” rifle (assuming a 40% increase over a 5” test barrel, and 25fps per inch over 16")
125gr at 2480fps - 1710ftlbs
158gr at 2165fps - 1644ftlbs
170gr at 2060fps - 1600ftlbs
180gr at 2060fps - 1695ftlbs
Now again, these are only rough projections, but comparing to the classic 30-30 Winchester we see (from a 24” test barrel)
150gr at 2390fps - 1900fps
170gr at 2200fps - 1825fps
If we drop the minimum 25 fps per inch to go to the 20” barrel we see
150gr at 2290fps - 1745ftlbs
170gr at 2100fps - 1665ftlbs
25fps loss from the 24” barrel is I think rather optimistic, I would expect something like twice that much velocity loss; with the attendant loss of energy.
So from comparable barrel lengths, you can see that hot loaded .357 delivers nearly as much energy as the .30-30… at least within the first 100 yards or so (the ballistic coefficients of pistol bullets are awful). This would also make it similar in power to 7.62x39.
Also remember, these are HOT loads, but they aren't even close to maximum loads that you can get with decent handloading (of course the same thing could be said about the other two comparison calibers).
Basically, this is a perfectly adequate caliber either for personal defense, or for hunting medium game at short ranges (under 200 yards maximum for small deer, 100 yards preferred).
The other example I want to use is the MechTech Carbine Conversion Unit, which has a 16" barrel. MechTech publishes data that show theres about a 30% increase in velocity over a 5" automatic in the standard calibers and loadings, and a 40% increase from the 10,mm .460 Rowland, and .45 super (when loaded specifically for the carbine again, not using standard pistol loads); so our approximations can hold here.
So lets assume we're dealing with 10mm here, since it's probably the best standard auto pistol offering for hunting.
Here's the loadings doubletap is offering.
135gr at 1600fps - 767 ftlbs
155gr at 1475fps - 750 ftlbs
165gr at 1425fps - 744 ftlbs
180gr at 1330fps - 707 ftlbs
200gr at 1270fps - 715 ftlbs
Those loads are solid, but you can do better with handloading. Applying the approximation to them we get:
135gr at 2240fps - 1505 ftlbs
155gr at 2065fps - 1470 ftlbs
165gr at 1995fps - 1460 ftlbs
180gr at 1860fps - 1385 ftlbs
200gr at 1780fps - 1410 ftlbs
I'd also like to add in a load I know to be safe for the 16" carbine, but which is well over standard pistol pressures.
220gr at 1880fps - 1730ftlbs
Though I have to say, I wouldn't load that in fired brass, or reload a case fired with that load.
So you can see, the 10mm carbine can be perfectly adequate for those same medium game at short ranges.
Of course anything thats good on a deer out to 200 yards, will be good on a man out to around the same ranges.
Oh, and just for comparison, lets look at the standard 5.56 nato loadings from a 20" barrel:
55gr at 3250fps - 1290ftlbs
62gr at 3025fps - 1260ftlbs
Lose four inches, and from experience I know we're going to lose on average 250fps going from the 20" barrel to the 16" barrel.
55gr at 3000fps - 1100ftlbs
62gr at 2775fps - 1060ftlbs
Now we can't make a direct comparison of energy numbers here; because as Martin Fackler has proved there is a qualitative difference between wounds created by projectiles traveling below approx. 2500fps or so, and those above; where the temporary stretch cavity tends to be more seriously damaged, partially changing to a permanent tear cavity.
That said, I would expect the wounding effect from the 16" barrel lengths at short ranges to be similar for the 10mm carbine with hot JHP loads, and the AR platform firing either of the standard NATO chamberings. In fact, I would expect the 10mm to be a more effective hunting cartridge at short range, because of its greater mass.
Oh, and for those interested in serious big bore carbines, there are certain .44 and .454 loadings that will break the 2500fps threshold out of an 18-20" barrel; and most .460xvr loads will do it.
The standard .460xvr loading hits 200gr at 2350fps from an 8" barrel, and should approach 2900fps with a light weight bullet (I would guess 165gr would be about the minimum), a slow powder, and an 18" barrel.
Assuming it COULD be done, the energy would be ridiculous at 3000ftlbs which is approaching .300 win mag power levels. Even if only 2800 can be pushed out, you could still match the 7mm magnum.
