Slower In '73 Than In '73?

Shotgun Franklin · November 05, 2014, 10:45:39 PM

I got to try my reloads over a chronograph last weekend. It turned out my '73 rifle shows lower muzzle velocity than my Colt '73. This was the first time I'd actually experienced this. It happens because I'm shooting pistol ammo through a long barrel rifle. In the revolver the bullet leaves the bore shortly after the powder has done it's job. In the rifle the peak power ends well before the bullet leaves the barrel and friction slows the bullet in that long barrel, anyone less had this happen? It's more pronounced with a fast powder and I'm using Red Dot which is fairly fast.

Tommy Reb · November 06, 2014, 01:03:51 PM

Hello Shotgun. Only cartridge I have ever seen this for myself is with the 22 LR. However, it could happen with other cartridges, I suspose, for the reason you outline. What is the chambering of your '73's? Did you make the velocity measurements from both guns near the same time of day with the same chronograph spacing? Were the velocity standard deviations/extreme spreads relatively low for both guns?

I have '73 rifles and pistols chambered each in 357 Mag, 44-40, 45 ACP and 45 Colt. Using lightly loaded CAS rounds (except for the 45 ACP which are Wild Bunch ammo at a power factor of about 160 in the 1911), the rifles all show at least 125 fps more velocity than the pistols. That is using Green Dot powder which is just a tad slower than Red Dot.

Interesting observation. Thanks for posting.

TR

Shotgun Franklin · November 06, 2014, 01:56:41 PM

Both guns were .45 Colt. Fired at the same set up only a minute or two apart. I have read and heard of this happening but when you see it, it's still a surprise. Oh, one shot each gun, it was just before shooting a match. My '73 is the rifle, I'd expect a bit less difference in a carbine but I don't know how much?

wildman1 · November 06, 2014, 02:34:32 PM

Can't tell much from one round. Try at least 5 in both and see what the dif is. wM1

Shotgun Franklin · November 06, 2014, 04:14:54 PM

When it's someone else' machine and you're allotted one round per gun then that's what you do.

treebeard · November 06, 2014, 05:53:32 PM

Has anyone tried this in a carbine as opposed to a rifle length barrel? That four inches of barrel might change the result.

Cliff Fendley · November 06, 2014, 06:57:36 PM

I wouldn't trust anything less that a 5 shot string of a particular ammo in each gun and a couple or more strings to compare is even better. I always test ammo and guns in at least a five shot string and look at the SD and ES. If you have a wide ES you can check each shot to see if one is way off.

If you notice any funny business trying different positions and looking at ES/SD can tell you if you have other issues to look at such as a powder that is position sensitive in big cases like the 45 Colt with the light loads of smokeless used in CAS.

How was the revolver positioned before you leveled it out to shoot? Was the muzzle up before you leveled it out and cocked it leaving the powder back against the primer? Was the rifle fairly level as it was chambered and was it chambered slow or at a speed fast enough to shake the powder to the front leaving no powder against the primer?

Too many variables could be in play. I chronograph most everything I load and shoot and being a tinkerer like to try different things, you would be surprised at how disturbing some of the results can be on many of the loads used for CAS. Very good possibility you could do the same thing again and get different results.

cpt dan blodgett · November 06, 2014, 08:58:33 PM

Several variables, if a light load and fast powder the volume of gas produced may not be sufficient to cause acceleration all the way down the bore. If the bore of the rifle is not as tight some gas may escape around the bullet, spin rates of rifling could potentially effect velocity

hp246 · November 07, 2014, 05:06:01 PM

With only one round, a light powder drop could account for that one round being slower.

Shotgun Franklin · November 07, 2014, 06:46:06 PM

6.7 gr Red Dot, 200 gr lead bullet

yahoody · November 25, 2014, 10:27:10 PM

Quote from: Cliff Fendley
I wouldn't trust anything less that a 5 shot string of a particular ammo in each gun and a couple or more strings to compare is even better. ... look at the SD and ES. If you have a wide ES you can check each shot to see if one is way off.

Too many variables could in play.

this