Do rifle crowns matter? Does a crown affect accuracy? I find out with the help of my grinder…

Do rifle crowns matter?  Does a crown affect accuracy? I think most of use would say yes.  It seems intuitive that the crown, the last part of the rifle that touches the bullet before it leaves the barrel, should be precisely cut and free of burrs.  I’m partial to an M40 style crown, but there are a lot of good options.

The crown debate goes beyond basic machining.  With the proliferation of Cerakote, some shooters often wonder if some finish that found its way into the barrel can destroy the rifles ability to shoot well.  While in the field, hunters are cognizant to not create a nick or burr in their muzzle if they are in rough terrain.

As odd as it may seem, over the years I’ve shot some great groups with some bad crowns.  Let’s take a look at some of these bad crowns.

Back in 2013 I started conducting some barrel length and velocity experiments.  It all started with a 300 Winchester Magnum and the #8 Shilen Select Match barrel sown above.  We started cutting back the barrel with a reciprocating saw 1″ at a time to start our data set.  On a lark, we decided to shoot some groups…

19.25″ and 20.25″ barrel length groups.

We were shooting Federal Gold Medal 190 gr ammunition.  What was most interesting was despite the fact that the muzzle was chopped off in such a harsh fashion and the muzzle was not deburred, let alone crowned, the rifle still shot fairly well.  Check out the two five-shot groups above, .930″ (.888 MOA) and 1.372″ (1.310 MOA, shot from butcher-crowned rifles.  Conventional wisdom would say we shouldn’t be anywhere close to an MOA.

A representative crown. Shockingly, this crown produced a .744″ 5 shot group at 100 yards!


This 5 shot group was fired from the 17.25″ hacksaw cut barrel!

Once the battery died on the reciprocating saw, we switched to a hacksaw.  Again, the rifle still shot surprisingly well.  Above is a 300 Winchester Magnum with a 17.25″ barrel and a hacksaw cut, non deburred crown!

Those early lessons weren’t lost on me.  If you dig around you can find tests like this one from Shooting Sports USA.  While it is worth noting the data set they collected is not included in the article, the author contends that crown damage will affect accuracy.  This seems to make sense.

When I began to work on my 224 Valkyrie barrel length and velocity post, I decided to shoot some groups.

As a reminder, the test rifle was built with the following parts on my Precision Matthews PM-1440GT lathe.  It includes:

Even though this rifle was built to be cut up, it still handled very well.  The new MDT LSS-XL GEN2 chassis is outstanding, especially when it is coupled with the Skeleton stock.

When I ran the test, I decided to shoot some groups with the 60 gr. NBT loads at 100 yards.

First up, I shot the barrel with the end as it came form the factory.  Note the band mill cuts and the 60 degree center cut in the middle of the muzzle.  This is anything but a quality crown.  I wonder how it will shoot?

  Boom!  That’s five rounds at 100 yards into .575″ (.549 MOA)!  That’s factory ammo from an essentially “crown-less” barrel.  Hmmmm, who’d have thought that would happen?

As I expertly used my cutoff wheel to chop down the barrel I kept shooting some groups.


Interesting, with these awful grinder-cut crowns, I still ended up with a bunch of groups right around 1 MOA.

That lead me to the question: how bad does a crown have to be before it stops shooting well?  I broke out the grinder and this is what I came up with:

OK, this isn’t my finest work.  In fact, you’d be hard pressed to do a worse job.  It’s not straight, square, or smooth.  To say that “it’s rough” is an understatement.  In fact, its kinda pointy, like an integral bayonet on my barrel!  Might as well shoot it.

Turns out the cut shifted my point of impact (POI) about 16 MOA.  I fired 4 rounds at 50 yards to refine my zero and swung over to the 100 yard target shown above.  I fired six 5-shot groups prone, from a bipod with a rear bag.

Group sizes, measured center-to-center, were .696″ (.665 MOA), 1.453″ (1.388 MOA), .885″ (.845 MOA), 1.229″ (1.174 MOA), 1.231″ (1.176 MOA) and 1.139″ (1.080 MOA).   Average group size was 1.106″ (1.056 MOA)!  That’s not too bad for a rifle using factory ammunition; factor in the horrible crown and I am pretty impressed.

NOTE: If you are a regular reader you’ll note that my target looks different.  I used to use 1″ orange dots on cardboard targets.  They worked in most conditions, however, in heavy rain or extreme cold, the adhesive would fail and they would fall off the target (see the orange dots in the target above).  I developed this target with Rite in the Rain.  It is on waterproof stock with true 1.047 MOA green dots.  The color provides excellent contrast and you can still see your impacts on the paper.   Rite in the Rain sells these targets as well as paper that you can print your own targets on.   To learn more about Rite in the Rain and their line of targets, click here.

It is worth noting that the POI did change slightly from the first group to the last group.  I don’t have an explanation for it.  Could it have been the crown? Maybe.  Could it have been something else? Possibly.

Let’s answer some big questions…

  1. Does a rifle’s crown affect accuracy?  Yes, it can.  Bear in kind what accuracy means,  how close we are to the target.  We can have a precise rifle that isn’t accurate and an accurate rifle that isn’t precise.  If you have a zero on your rifle and damage the crown you’ll most likely have a POI change which in turn affects accuracy.
  2. Does a rifle’s crown affect precision?  Not necessarily.  I think the take away message from this post is that you can do some pretty awful things to your muzzle and still have a rifle that groups fairly well.  Am I shooting 1 and 2″ groups?  No, but I’m not about to do any load development on this gun.  Would I want to take a rifle with these crowns to a match?  No way.  But it sure is interesting to see how well a tube like this can shoot!