Shortening barrel length

Although the actual act of cutting the barrel goes into more detail here: LOW BUDGET .22 SIL. RIFLE/TRAINER - shortening the barrel , this post goes more into the range report differences of shortening the barrel.

Whether you call it a 20" barrel as advertised, 19.75" measurement from the muzzle to receiver, or 21 1/8" by inserting a cleaning rod into the barrel againt a closed bolt, then marking and measuring the rod, we'll call it the "stock length barrel", -1", and -2".

Rifle used: Savage MKII "F" sporter barrel - 2lb 12oz trigger - shot of harris bipod and rear bag - 12x on the optic. Used 2 ammos, CCI blazer (high velocity) and Aguila Golden Eagle Match rifle. 10 round groups were shot, barrel was dry swabbed "clean" before an ammo change. At 50 yards, 1" bull was used, at 100 yards 1.5" bulls.

Groups with the stock length barrel - weather 65 deg. F., 35% hum., 3-7 mph wind from 8:00, mostly sunny.

Groups with the -1" and -2" - weather 45 deg. F., 47% hum., 3-10 mph wind gusts 3:00.

FPS per length - Chrony was set at 10 ft away from muzzle:

Stock barrel

Blazer - 1241 FPS avg., (range of 1221-1256 FPS)
Aguila Match Rifle - 1101 FPS avg., (range of 1080-1126 FPS)

-1" shortening

Blazer - 1216 FPS avg., (range of 1207-1221 FPS)
Aguila Match Rifle - 1083 FPS avg., (range of 1062-1095 FPS)

-2" shortening

Blazer - 1217 FPS avg., (range of 1173-1239 FPS)
Aguila Match Rifle - 1082 FPS avg., (range of 1062-1111 FPS)

50 Yard groups - stock length top, -1" middle, -2" bottom

[img width=335 height=450]http://i633.photobucket.com/albums/uu54/WALTERRO/mkii%20barrel%20stuff/barrellength50yd.jpg[/img]

100 Yard groups - stock length top, -1" middle, -2" bottom

[img width=335 height=450]http://i633.photobucket.com/albums/uu54/WALTERRO/mkii%20barrel%20stuff/barrellength100yd.jpg[/img]

It appears (in general) that the groups of both the ammos shrank at both 50 & 100 yards. From stock length to -1" there was a 25 FPS drop in the HV Blazer, and 18 FPS in the Match velocity Aguila. When shortened another inch to 2", no significant drop in FPS, but more consistant on paper. Oddly the -1" and -2" barrel length RAISED the POI an average of 1.5" in the HV and remained the same for the match ammo at 50 yards. On the contrary, at 100 yards the POI on the match ammo changed about 1.5" higher - STRANGE!

BULLET DROP - (shooting at 100 yards with the 50 yard setting) the amount of bullet drop changed, but only slightly by about -.75" with the shorter barrel.

OVERVIEW:

1. Shortening the sporter barrel decreases group size with HV and match ammo.

2. FPS was reduced with the initial -1" (around 20 FPS), but the second inch reduction didn't show much more as i would have expected (I figured it would be -40 FPS, but was nearly identical to the -1" FPS).

3. Balance and handling was improved.

So will further shortening the barrel decrease group size more, stay the same, or actually hurt?

After the initial drop in FPS, wouold FPS stabilize until a more "extreme shortened barrel" length is reached?

Is it that the shorter barrel is "stiffening" up the sporter styled barrel by reducing "whip" and harmonics producing better groups?

I'm not sure at this point, but shortening my sporter barrelled rimfire by 2" actually improved my groups at both 50 and 100 yards, high velocity and match / standard velocity.

Although I'm tempted to shorten the barrel more, I find it best to stop here on the side of caution - for now. If there is a certain point where shortening a barrel starts to detriment performance, I don't want to find it, 'cause when you pass it, you can't add more barrel. I've heard many having success with a 16" barrel, but for now my 2" inches off will serve me well - at least until I bug myself enough to go to 16". If I do, I'll update with the results.