Chronographed .45cal PRB loads today

[roundball]

EQUIPMENT

TVM Early Virginia
Rice 42” B-weight swamped barrel
.45cal x 1:66” x .016” round bottom grooves
Chambers Deluxe Siler
Davis DST

SHOOTING PARTICULARS

Cleaned / dried / lubed the bore after every shot
Pact Pro MK5 Chronograph at 15 feet
Goex 3F powder
.022” OxYoke precut/prelubed patches
Hornady .440 balls

5 shot group average velocity rounded off to nearest 5 fps
70grns = 1535 fps
80grns = 1710 fps
90grns = 1810 fps
100grns = 1865 fps
110grns = 1960 fps

I never understand the occasional non-linear size step from one powder increment to the next…like the one from 90 to 100grns…but have seen similar odd steps in other rifles over the years…and repeating the group today gave the same kind of step result.

Was also impressed to see velocity continue to climb in this long, slow twist barrel and the 110grn charge actually had a couple shots in the string break 2000 fps.

Felt no difference in recoil trying 100 / 110grn charges…hefty, accurate rifle, a pleasure to shoot.
NOTE: 110grn charge makes an audible ‘crack’ sound…next range trip I’ll check it for accuracy.
If it’s as accurate (or more so) than 90grns, I’ll just use 110 for my deer load instead of 90.

[doug.brayman]

That's interesting. I have a 38" green mountain. I am getting about 1800FPS with 65gr of 3f and about 1900 with 75 gr using .495 ball with .018" patches lubed with Murphy's oil, hydro peroxide and alcohal. A jump to 80gr of powder had almost no effect on velocity.

[roundball]

My chronograph results are always lower than other peoples...I assume there must be some sort of sensitivity issue with it.
Not much else I know to do other than set it out at the length of its 15' cables to eliminate smoke interference, shoot through the screens, and read the display...LOL.

[ramrod]

roundball did you ever chrono.  32" green mount. bbl. in 45 cal. am curious as to results as i plan to use a thompson center in pa. early season in perc. just trying to get ideas as to limits of 32" bbl.  thanks

[roundball]

That's interesting. I have a 38" green mountain. I am getting about 1800FPS with 65gr of 3f and about 1900 with 75 gr using .495 ball with .018" patches lubed with Murphy's oil, hydro peroxide and alcohal. A jump to 80gr of powder had almost no effect on velocity.

I meant to ask, if you don't mind saying, what brand of chronograph do you happen to use?

[mulefour]

Have you ever tried different vent sizes?

[Buzzard]

My 42" Montana barrel is getting 1800fps with 70gr-3f and prb.

[hanshi]

My 36" barrel approaches 1800fps with 70grns of 3F.  All my chronographing is done with an Oehler and 4" bar with the "third eye" screen.

[roundball]

roundball did you ever chrono.  32" green mount. bbl. in 45 cal. am curious as to results as i plan to use a thompson center in pa. early season in perc. just trying to get ideas as to limits of 32" bbl.  thanks

Sure haven't

[roundball]

Have you ever tried different vent sizes?

No, same type vent on all my long guns...has a .070" vent hole...probably a little larger than some...maybe a bit more pressure loss there?

These are the results from a 42" x .45cal GM barrel in 2010, same vent, almost identical.
Average velocity rounded off to nearest 5 fps
40grns = 1270 fps
50grns = 1430 fps = +160
60grns = 1550 fps = +120
70grns = 1670 fps = +120
80grns = 1785 fps = +115
90grns = 1900 fps = +115
100grns = 1950 fps = +50
110grns = 1975 fps = +25

[hanshi]

Interesting comparison.  It's easy to see where the point of diminishing returns starts.

[doug.brayman]

That's interesting. I have a 38" green mountain. I am getting about 1800FPS with 65gr of 3f and about 1900 with 75 gr using .495 ball with .018" patches lubed with Murphy's oil, hydro peroxide and alcohal. A jump to 80gr of powder had almost no effect on velocity.

I meant to ask, if you don't mind saying, what brand of chronograph do you happen to use?

Roundball, It was a friends chrono and I dont remember the brand. I will have to check on that and get back to you.