If you were machining a crown would you want it square?

[NickG]

Hoy ......


Clear off you Rotter .

Did I say something logical ?

[Solvo]

The best reason to machine the crown square is that anything other than square needs to be concentric to the bore.
Short of buying some very expensive parallel rods used for clocking up a barrel to the bore it's near impossible to get it perfect.

Machine square and you can be concentric to the OD with whatever accuracy your 3 jaw or collet has without any worry about how it will impact the accuracy.

Lots of different shapes have been used over the years in firearms and air rifles, they mostly work to achieve a balance between ease of machining and durability.

The bull nose rounding seen on many springers is very durable and wont get damaged if the muzzle knocks the ground. Steyr use a double step where the crown is square but recessed a few mil, same result overall but easier to machine to the required accuracy on a CNC.

[hmangphilly]

Did I say something logical ?

Yes mate .
Beat me to the point .

Only far more succinctly than my old waffle .

[PhatMan]

Hello to All,

Juts had a quick peek in the Interweb :

Some tests here : http://www.accuratereloading.com/crownr.html

From http://forum.accurateshooter.com/thr...stion.3804295/ (mentioning the Precision Shooting Tests) :

March 2011 issue. .308 HB model 70...w/ fresh 11' crown 5-shot group =1.02"....w/ notch in crown @12 o'clock w/ dremel tool 5-shot group = 1.15 (mostly vertical)....dinged crown at a land with a pin punch enough to cause serious burr with metal protruding into bore, 5-shot group =.68"....half-moon cut around 1/8 of crown circumference gouging it with carbide tool, 5-shot group = .75". Finally after dinging more of the crown AND gouging the inside of the bore 1/2" deep they netted a 1.75 in group for first 5 shots....BUT the next 5-shots were .700. Go figure. ???

In the July 2000 issue they tested muzzles that were not perpendicular to the bore. One @ a 12' angle facing up and to the right, crowns finished by using JB and a brass round head screw spun in a drill. The groups from the cocked crown followed the direction of the muzzle. The factory crowned .222 TCR'83 yielded a 5-shot group of .87 moa, the cocked crown yielded a two groups that averaged .70 moa, 3-1/4" above and right of POA. Finally, the author cut the muzzle square, lapped in the crown using the JB_brass screw, and netted .72 MOA groups.
I really miss the PS rag, the issues prior to 2009.

Have fun & a good weekend

Best regards

Russ